I think the phone will come locked to O2 unless you buy one off Ebay which has been unlocked. This is what I did, and then I upgraded to WM6. I have also got a SP5 which at the moment I still prefer. Reasons are as follows:
Although the graphite has a much faster processor- it doesnt seem any quicker in normal use. It just gives better benchmark results.
Battery life not as good as SP5, I dont think it will last more than 36 hours, of usual use. SP5 will last 48 hours. (few calls, few sms, some WiFi browsing, not excessive or constant use)
Speaker far too quiet, and its on the back of the phone. So when you get a call, its very hard to hear the ringtone, and if the phone is in a case, or in your pocket, you'll probably miss the call!
There's no IR. Bluetooth is not reliable for transfering files especially to a pc or another phone, but IR could always be used on the SP5.
Internet Explorer on WM6 is sooo slow when browsing large pages, such as the normal Modoco home page (not LoFi). the page will load ok, but as you scroll down either with the joystick or the 2 and 8 keys, the scrolling gets slower and slower, so that by the time you get to the bottom of the page, the scrolling is at a snails pace. This doesnt happen on the SP5. I installed the Opera browser trial which is lightening fast but isnt always as clear as PIE. The pages on Opera dont always resemble how the website looks on the desktop.
The remaining battery life is not as precisely shown as in WM5 (or WM2003). It starts at 100%, the drops in 10's to about 50%, then to 31% (?) , then to 22 %. There is no gradual drop. The SP5 would show the remaing battery much more accurately.
WiFi range isnt as good. Activesync 4.5 has to be installed on your PC and this doesnt seem as good as previous versions of Activesync.
On the plus side, the new operating system looks good, refreshed icons,tones and colour schemes. The screen is bright, much brighter than the sp5, and the joystick feels very firm. The camera is good but the video resolution is very low, which is a shame as the processor is faster. i am still not using the Graphite as my main phone and may just by a Pay As You go 3 sim to try on the 3g.