From what I last heard (I work in the industry) T-Mobile have been sending the updates out in bursts. We still see alot of phones with One2One on the screen, probably more than T-Mobile. Alot of T-Mobiles official documentation still has 121 on it!
They have been having a few computer problems lately as regard to new customers, don't know if this could have any effect on the update but you never know.