I finally got my trusty old 7105t unlocked. I deleted the T-Mobile service books, logged into the AT&T BIS page on my home computer to change devices by entering the 7105t's PIN and IMEI, and sent my service books. Boom! Up and running immediately, just like it should. Full functionality. Of course the 7105t never did MMS due to the lack of a camera, but it does everything else. No html email due to the OS being so old: 188.8.131.527
I'm totally loving the nostalgia factor here. SureType takes some getting used to again, but it's fun for now. And I have my precious thumb wheel back, which I have missed dearly.
I have two alternate wallpaper pics saved, MaraTick for shopping list, Google Maps, and Berry 411 Search installed, and that's it. This thing is as stock as can be. I have a whopping 10.6 MB of free memory upon reboot and it's generally fast and smooth operating.
I'm practically Michael Clayton here! (5 points to anyone who gets that reference)