The Skype client was released earlier this week for Apple's , letting users call other Skype users for free or landline or mobile phones for a small charge. But they can only do so over Wi-Fi networks, not the cellular network of the iPhone's sole U.S. carrier, AT&T.

In a to FCC Acting Chairman Michael Copps, Free Press lawyers cited a variety of press reports as evidence that wireless carriers may be violating the FCC's Internet Policy Statement, by restricting or crippling applications, services or devices, hindering consumer choice "for anticompetitive purposes."

The letter specifically cited the Skype example on iPhone, including a reference to a recent "USA Today" story which quoted an AT&T executive saying "We absolutely expect our vendors [e.g., Apple] not to facilitate the services of our competitors." The letter cited other examples of restrictions such as the banning from Google's Android Marketplace any applications that would let notebooks be tethered to the Android-based G1 phone from T-Mobile.

"These two cases suggest that the future of wireless innovation will be determined first and foremost not by developers of the devices, but by wireless carriers through restrictive language used to control consumers' use of applications and services on their networks," according to the letter.

Carriers such as Clearwire have defended various restrictive practices on the grounds that they need to prevent customers from tying up bandwidth with file-sharing or similarly demanding applications. Deutsche Telekom, the iPhone carrier in Germany, said it may block all Skype usage, including that over Wi-Fi