Why do they 70 million customers and keep adding new users while other so carriers keep loosing millions of subscribers?
Of the big US four, only Sprint is losing subscribers. ATT, Verizon, T-Mobile continue to gain at Sprint's expense. The prepaid resellers like Virgin also suck away new customers from everyone.
Verizon continues to usually have the most profit, and least churn, despite customers who moved to ATT for the iPhone... because they have the most postpaid subscribers (the best kind).
ATT has taken a profit hit for a couple of years, because of giving out 900 million dollars in (mostly) iPhone subsidies.