You can use the Verizon 9650 on TMobile. But you will need to MANUALLY load the TMobile Service Books.
Read this. Follow ALL the steps. HowTo:Get All Features (Browser, MMS) Working on T-Mobile w/Unlocked Storm 95xx - BlackBerry Forums at CrackBerry.com
It says "Storm" but it will work for the 9650.
Also you will need to change your data plan to a BlackBerry Data Plan.
Note also that you will not get 3G. EDGE only. But it will work.