
Overall: Great phone with good organizer features and messaging. Excellent form factor and innovative keyboard is very easy to use. Build quality seems very good, although the first one I received had a "Back" button that did not work, a manufacturing flaw. The replacement arrived overnight and is fine.
Pros
Excellent call quality. First and foremost, the M600 works very well as a phone. I am on T-Mobile.
NO CAMERA. This was a primary factor for me, as I cannot have a camera phone at work.
Great form factor. Unlike a lot of Pocket PC phones, this one is small enough to carry easily.
Multiple input methods. You can use the "rocker" keyboard, which works great, the pop up virtual keyboard, or character recognition. I think that only Sony-Ericsson is still doing character recognition you simply write on the screen with the stylus and the program types the letters. Way cool. What is a "rocker" keyboard? Well, it's not anything to do with rock-and-roll! Each key has two letters on it, and you push one side or the other to get that particular letter. An "ALT" key supports alternate letters above the normal ones. It is very fast once one becomes accustomed to the letter positions.
Cool interface. Obviously, the UIQ 3 operating system takes some getting used to, especially after a Pocket PC device. But it looks good and works well. Be prepared for a learning curve. For example, dialing a number is as easy and pushing the numbers there is not phone "application" such as one finds in the Pocket PC Phone world. However, this is only possible one the main "Standby" screen. In general, this device seems more "thought out" and "integrated" than a PPC. Consider it more of a MAC than a PC.
Excellent support. Sony Ericsson has a way to send a text message to configure the internet options on the phone. Very painless. It was equally simple to update to the latest firmware. If you get this phone, be sure and get the latest firmware it allows one to eliminate menu animation, which makes the OS much faster at rendering the menu screens.
Great battery life. I get 2 to 3 days of normal use. My old PPC got two days at best.
Support for Java programs.
Touch screen, which is unusual in a smart phone. Only some games support this feature, but I found a great bowling and pool application that work with the stylus.
The included games are pretty good, especially the Golf game.
Includes programs to view and (sometimes) edit Word, Excel, and Powerpoint documents, as well as a PDF reader. The feature set is somewhat limited in Excel, and I actually had to change some formulas in one of my spreadsheets in order to get it to edit on the device. It definitely won't do any database statistical functions. If the Excel reader doesn't support any of the formulae in the spreadsheet, it only opens in a "viewer" mode, with no editing possible. For those with a need for complex Excel or Word documents, there is no better device than a PPC naturally, since MS makes Windows Mobile 5 and MS Office. But the included programs work well enough. There is also a $50 program called "Documents to Go" that has better support, including database Excel functions. I ended up forking over the bucks for this program, and it has been worth the money.
Includes support for "push" email (like a Blackberry). I do not use the phone for corporate purposes, so I haven't used this feature. It is a separate program that has to be installed.
Supports POP, IMAP, and SMTP authentication. The inbox will store message headers forever until they are deleted from the server. Once they are deleted on the server (typically by your PC email program), the next time the M600 synchronizes email it will remove the headers. If you download a message there is an option to "delete locally", which deletes the body but still leaves the header. If you delete the header, it deletes the email on the server. This takes some getting used to. You can schedule periodic automatic email checks separately for each inbox.
Supports both text messages and Multimedia Messaging (MMS).
Supports a 2 Mb Memory Stick Micro card, to store plenty of data or music. The card is hot-swappable, on the outside of the phone.
Integrated video and music player, plus software to transfer songs to the phone. Supports DRM (which can be considered either good or bad).
Includes backup software to allow one to back up the phones memory to the PC.
The phone will optionally charge from a USB cable if desired. I prefer to let the battery get to around 20% and then power the phone off and fully charge the battery. It charges very rapidly around 1 hour or so. A wall charger (European with American adaptor) is included.
UMTS (high speed internet). This is a 2700 Mhz band used for high speed data in Europe only. BE SURE TO TURN OFF SEARCH FOR UMTS IF YOU ARE IN AMERICA the UMTS search eats up a lot of battery. The phone can be set to only search for GPRS, which is the slower protocol.
Includes Bluetooth support, including handsfree. The handsfree works VERY well.
Contacts can be added to one of nine quick dial buttons, and each contact can have multiple phone numbers and a photograph assigned, plus Email addresses and (in general) just about anything else that MS Outlook supports. Ringtones can be added from MP3 files stored on the phone.
Voice dialing and answering is fully supported, only in handsfree mode.
Cons
Tri band. This phone does not support the 850 Mhz frequency used by Cingular (AT&T). It works fine on the T-Mobile bands. However coverage will be best around interstates and large cities. Some people prefer the "Quad Band" phones, which will roam on more networks here in the US.
No WiFi capabilities.
NO CAMERA. I know, I already listed this as a "Pro" item, but many people want a camera on their phone. Not on this model! However, the upcoming Sony Ericsson P1 is the same form factor as this phone and includes both a camera and WiFi.
No EDGE support only GPRS, which is slower. Think of it as a 28 baud modem, and that is the correct speed. However, WAP sites load fast enough using the built in browser, which loads smaller pictures of websites by default.
The voice dialing does not include "character recognition". This means that one has to go into each phone number and record the contact information exactly as one will say it to do hands-free dialing. Be aware that voice dialing only works with either the corded or BT handsfree attached.
No profiles. Most devices have (at least) built in profiles, or customizable profiles. Thus one could set the phone to "handsfree profile", and automatically turn on the BT, etc. This phone doesn't have this feature.
Unable to customize the main screen. In the M600 this is the "standby" screen, and the only thing that can be customized is how much of the calendar and messaging one wants to display. One can change the five icons across the bottom, but that is it. Coming from the PPC world of Windows Mobile 5, where the entire "today" screen can be optimized, this is a bit of a disappointment. No "plug-ins" allowed!
Relatively low memory. I have not run out of memory yet, but I am careful to close all applications after I use them. Like the PPC, this device will leave programs in memory, not actually close them. However, it is much simpler to close the programs than on the PPC. The device really should have come with 128 mb, like most of the competition. Note again that the new P1 will have 128 mb of memory.
The included web browser (opera mini) basically uses up the entire memory of the device.
The device can occasionally lock up. I have had this happen while adding voice dialing to the contacts, and once when I tried to make a call while the phone was just finished with another call. In each case I recovered by turning the power off and on. It has only happened three times, which is way better than my old WM 5 PPC phone, which locked up and misbehaved all the time.
VERY tight battery cover. OK, this is a bit picky, and I know they are trying to get good tolerances in their construction, but the battery cover took a LOT of pressure to get off. I finally found that if you hold the phone upside down and use the right thumb at the base and the left thumb at the top of the battery cover, the cover can be removed but it is still difficult. If you plan to switch batteries a lot, you might keep this in mind.
The SIM card fits under the battery cover, and is nearly impossible to get out without tweezers. This isn't too big an issue, since 1) you can't remove the battery cover anyway [little humor there], and 2) you seldom switch SIM cards anyway.
I synchronize my calendar with Outlook XP, and I found that my repeating annual appointments will duplicate in the phone and in Outlook if I connect the phone to the computer while Outlook is already running. So I have to be sure to close Outlook before connecting the phone. I had about 10 copies of everyone's birthday when I realized what was happening. Deleting them was, to say the least, very interesting. I ended up deleting a couple of birthdays entirely and re-entering them.
Summary:
If you are tired of large devices and MS nonsense, this phone is for you. You have to get to know the OS, and the whole point is that it ISN'T that customizable but it is stable and dependable.

Well, I selected this phone after buying my wife a 910i last Christmas and seeing how good it was, decided to drag myself in to the 21st century :)
I wanted something a little smaller (previously had a T39m) and this unit is great, and suits my work profile as I cannot visit Customer sites with a Camera phone this phone does NOT have one, and that's just what I need.
Bought from Amazon and it DOES come with a QWERTY keyboard so ignore the reviewer above who, unfortunately got a QWERTZ layout (begs the question why not return it?).
Anyway, I'm more than happy with it it's a phone, organizer,web browser and email tool, all in one. Bluetooth and IR are extras I've not used yet may get a headset sometime though.
I use T-Mobile service, and for the $5.99 extra for T-Zones Web, you get access to email, and the FULL internet. Ok it's not blazing fast access like DSL or something... but good for quick web access when out and about. It has the Opera browser built in, and works very well.
As it's tri-band (with one band being 900Mhz) I think it's limited to GSM services from T-Mobile, Cingular now AT&T -, Maybe Verizon?, and some of the Canadian carriers. Check your service carrier for compatibility, some use 850Mhz in the US.
The touchscreen is easy to use. and the keys (whilst small) work really well. In fact I use these more than the stylus, though for web browsing you really use a combination of them both.
The display is bright an crisp and really bright indoors (which you can control), though outside in bright sunlight the display tends to "washout" a little.
One little "issue" to date, is that the updated synchronisation software from Sony Ericsson (v1.2.15) seems to blow away my laptop on occasion when removing the phone from an external CDS-60 cradle... That's the only reason it gets 4 out of 5 stars from me.
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I just got my M600i from Amazon. As soon as I opened the box, I was disappointed to see that:
1) The keyboard is QWERTZ and not QWERTY!!!
2) The charger is not a US charger. It has round prongs. However, an adapter is provided for US plug. OK, this is not so bad, but I'd prefer to not have to deal with an adapter since it's another thing that I can lose.
After I played around with it, I found a few more things:
1) Apparently this M600i is an Asian version, probably imported from Singapore. On the timezone setting, the original value is Singapore. And also on the language selection menu, the choices are UK English and Chinese (written in Chinese characters).
2) On the text entry setting, there's an option for Chinese virtual keyboard
3) There's an annoying floating palette that provides what I think is different mode of entering Chinese character. This palette shows up during text entry mode.
4) In the tools menu, they have an application called "Lunar Calendar" which is some kind of Chinese calendar
5) There's a dictionary application and there are only 2 translation available: Chinese to English and English to Chinese.
I wanted to flash the firmware and install a generic English language firmware. I used Sony Ericsson Update Service (SEUS), but SEUS said that the phone already had the latest firmware. I've been researching Sony Ericsson and Symbian forums but haven't had any luck.
So there you go... now you know better than I did. For me, the killer is the QWERTZ keyboard. This phone is going back to Amazon.
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I have been using this phone for over a year now. I love it. I usually keep it in my front pocket with change and whatever else happens to be in there and after a year it doesn't have as single mark or scratch on it. I'm amazed. It looks as new as the day I bought it. Beyond its duribility its funtionality seems to be just as durable. I haven;t had a single issue with it. Its easy to use, has eveything I need, and has been very reliable. Some of the issues pointed out in previous views, like not being able to define multiple profiles or customise the main screen, lock up issues, etc have been addressed with new firmware releases. And I have been able to run Blackberry Connect on it with great success to use it for my company email enterprise server and also push personal POP3 email out to it. Even my companies security policy changes recently pushed to all BB users were not a problem. I have nothing but good things to say, and I am very anal and super picky. Being a technophile i certainly puch all its features to their full extremes too. Best of all I have yet to come across anybody else with one in daily travels. So, wait...ignore this review and please don't buy one ;)
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I bought this phone thinking about another sonny ericsson I had couple years ago. There is nothing related to that one. Seems like this phone comes from another brand. Instead of improving they made it worst.
The features that come with this phone, don't work properly, but how did I was going to know it until trying to use each of them with time?
The instruction manual is incomplete.
It took me years to load music to it. The memory is small and it is not explained that it comes with one of this tiny memories that is great enough for two or three songs. After buying the 2G memory ($20 extra)I only could record music directy from an original disc... another of sony's great ideas. The music that was already in my computer marks error, can't be copied.
The phone sounds good and can be listened as a small radio.
The support page never offers real solutions either.
What I like is the big screen. I will hardly go back with a phone with a smaller screen.
A shame it doesn't have camera, but stiil it won't work properly for sure... I just give it two and a half stars as it works pretty mediocre.