Zach at the BoyGenius scored some inside info on this years upcoming holiday promotion from T-Mobile. They will be offering free companion tickets to those who activate, renew, or migrate to a new 2 year service agreement between November 19th and December 24th.
The promotion will go live November 19th and will offer you a free round trip companion flight when you purchase a full fare ticket through a special T-Mobile website, www.flywitht-mobile.com, which is not live yet. 112 origins and 110 destinations will be available as you can see in the image.
Zach details some restrictions but its mostly making sure you are on a regular non corporate prepaid account.