Following reader comments and questions, iLounge contacted AT&T to clarify ambiguous details on iPhone 3G service plans, which will be offered starting on July 11. We asked AT&T to clarify its stance on text messaging, which presently is included in AT&T’s $20 EDGE data plans for first-generation iPhones, but is not listed as an included feature in its $30 3G data service plan for iPhone 3G. Mark Siegel, Executive Director of Media…