Engadget posted some very interesting insight about the hearing that happened in Congress recently. A few bits of discussion:
One of the primary concerns in the hearing was determining whether or not AT&T actually has enough spectrum on its own. Think of spectrum like the number of lanes on a busy highway: during rush hour these highways get clogged up and causes traffic to slow to a crawl, but when more lanes are added, more traffic can be accommodated. Stephenson argues that one of the major reasons his company needed to purchase T-Mobile is to have enough spectrum to properly build out its upcoming LTE network.
The FCC’s 2008 auction of the 700 MHz band would like a word with you:
Block B – AT&T Mobility was the biggest buyer in the B block, with 227 licenses totaling $6.6 billion. U.S. Cellular and Verizon bought 127 and 77 licenses, respectively. AT&T Mobility and Verizon Wireless bought licenses around the country, while U.S. Cellular continued with its strategy to buy licenses in northern regions. 
This doesn’t sound like a company that’s particularly hurting for spectrum to me.
But the real reason why this is a bad idea is because this effectively creates a GSM monopoly in the United States. AT&T will be the one who gets all of the roaming revenue from foreign visitors, vs. the current situation, for one thing. (AT&T and T-Mobile are the two national GSM carriers in this country.) Not to mention that Verizon and AT&T combined will end up controlling 80% of the US mobile phone market in general.
Let’s hope that the FCC and DoJ hear your voice loud and clear.