Well, gosh, that was quick. I put in the order to have my number ported on December 10. After making several calls to Tmobile’s number portability center, I tried again late last night (when the hold times are shorter) and got someone helpful. He said “it looks like we’ve got concurrence, so it’s just a matter of finishing up the procedure.” Since I was being a squeaky wheel, he jumped me to the top of the work queue for that night, and a few hours later, my phone spazzed out and indicated that yes, in fact, it now answered to my old number.