Since its introduction last week, the Skype application for iPhone has become one of the most popular downloads at the Apple iPhone store.  But some are complaining that restrictions placed on the Skype application by AT&T and Apple are anticompetitive and quite possibly a violation of federal law.

Skype is  a Voice over Internet Protocol (VoIP) application that competes with AT&T’s own voice service.  By using Skype, iPhone customers should be able to sidestep AT&T, allowing them access to cheaper voice plans that offer fewer minutes. iPhone users can also save money on international calls by using Skype.

But the Skype application can’t be used on AT&T’s high-speed 3G wireless network. Apple, which has an exclusive deal in the U.S. with AT&T, says iPhone users can use the Skype service only at Wi-Fi hot spots.  Before Skype could offer its application at Apple’s on-line download store, it had to agree to these restrictions.

After the launch of the Skype iPhone application, AT&T’s top public policy executive said in an interview with USA Today that the company has every right to block Skype. As far as AT&T is concerned, Apple is expected not to promote or facilitate the services of AT&T’s competitors, the executive said.

But Free Press, a group that has long-advocated net neutrality,  doesn’t agree with AT&T’s assessment.  The group has sent a letter to the Federal Communications Commission (FCC) asking it to determine whether or not the restrictions imposed by AT&T and Apple are a violation of federal law.

In its letter, Free Press cited the FCC’s Internet Policy Statement which holds that  “consumers are entitled to run applications and use services of their choice” in order to “preserve and promote the open and interconnected nature of the public Internet.”  Those guidelines, which aren’t formal rules, say carriers should let subscribers have access to any legal Web content or service they choose as long as it doesn’t harm the network.