AT&T today posted one of its best-ever spring quarter results credited mostly to the iPhone 3GS launch. The company says it added 1.2 million cellphone subscribers, an all-time high for spring. It adds that it activated 2.4 million iPhones between April and the end of June. The number ties that of the iPhone 3G launch quarter but is considered a record as the iPhone 3GS and $99 iPhone 3G were o
