T-Mobile would clean up on this deal if the US Government succeeds. Look at that breakup fee: $3 billion in cash and another $4 billion in non-monetary benefits.
Included in the "non-monetary benefits", T-Mobile would receive access to certain AT&T spectrum (it actually reads as if AT&T would simply have to hand it over)...
This shared spectrum is something that has been sorely lacking in the U.S. and has been terrible for the consumer -- government granted monopolies are auctioned off to single companies and most devices will only work in a single company's spectrum band, however, if the spectrum T-Mobile gets is in the LTE band, this would have a significant positive impact on their service quality.
I thought it was a sliding scale. It links to the amount of divesture required of AT&T. At some point, the breakup fee goes to naught. (source: I thought I heard this on CNBC this morning ... don't see any articles online that confirm this. Maybe I was dreaming?)