AT&T just announced that they will purchase T-Mobile USA from Deutsche Telekom for $39 billion. This transaction – even after the FCC and DOJ force significant divestitures – will make AT&T the largest wireless carrier in the United States. This will leave AT&T, Verizon (NYSE:VZ), and Sprint (NYSE:S) as the big three wireless carriers in the domestic U.S. market.The wireless industry will have 12 months to figure out the implications of this deal, but it will…