I have unlocked my 8700c (costs nothing if you paid full price for the device, wait 30 days and then request the unlock code for your IMEI number, which takes 7-10 business days in theory) and I now use it with my TMO SIM as well as when traveling internationally.
- I have scratched up up and the black does show through
- I feel the TMO EDGE in DC is slightly faster than Cingular EDGE (maybe because they have not released many devices that take advantage of the network yet)
- I use many different Themes (current favorite is MacBerry, which emulates OS X on the BB), so the Cingular name is a minimal bother on the front of the device (the screen says T-Mobile when connected to the network)
I have used a BlackBerry since 1999 (yes, the very first RIM handhelds, not even deemed BlackBerries), and I can say this is hands down, the best BB I have used.