Originally Posted by nwaves
Flashing apps backed up with Ti on Froyo to Gingerbread is a sure way to run into troubles.
Easiest way for him is to root, install CWM, make a nandroid of his stock ROM and then flash CM7. If/When he decides to get service back, he can make a nandroid backup of the CM7, then wipe it and recover the Stock ROM, activate the phone and then flash the CM7 nandroid back.
Speaking from personal experience, I had no trouble backing up/restoring my 70+apps when I upgrade to GB. May be different from other people, but it worked just fine for me.