Coming off a lengthy exclusivity contract for Apple's iPhone, AT&T is undoubtedly concerned about its largest competitor receiving the popular handset. Today marks Verizon's official iPhone 4 launch and AT&T is looking to steal a little thunder from big red by introducing an unlimited mobile calling feature to new and existing service plans. As of today, qualifying AT&T subscribers can call any mobile number in the US without having to watch their minutes.

Surprisingly, you shouldn't have to jump through too many hoops and the offer includes a lot of members. Eligible voice plans include AT&T's Nation 450, 900 as well as FamilyTalk 700 or higher. To qualify for unlimited "Mobile to Any Mobile," customers will also require an unlimited messaging plan which runs $20 for individuals and $30 on family plans. Although there doesn't appear to be too much red tape involved, you'll still have to sign up.