It has been a long, hard battle for the AT&T/T-Mobile USA merger so far. They have faced a public who is reluctant to have only 1 GSM carrier left in the country, a Department of Justice lawsuit looking to prevent it and a leaked document revealing AT&T's real reason for wanting T-Mobile USA. Recently, the FCC got involved in the issues when the chairman recommended to his board that they disallow the merger.
AT&T's reaction was not quite what was expected but not terribly surprising. AT&T withdrew their bid for FCC approval completely. Now, this might seem to indicate that perhaps they feel they have failed, but I don't think that is what is happening here. With a major DoJ case coming up, their legal team needs to focus all of their attention there, not let it get spread across fighting two big battles. The easiest way to do that is to eliminate one of the problems. Done.
That's not their only reason for delaying the FCC. Hit the break to find out what else is going on.