Regulatory authorities in the US and Europe have been asked to investigate Skype's implementation on iPhone, specifically that it works via Wi-Fi only and not through a 3G connection.

That restriction has been described as anti-competitive and, according to the Wall Street Journal, the  Federal Communications Commission has been asked by an Internet advocacy group called Free Press  whether the restriction is in violation of federal law.

Free Press bills itself as a non-partisan organisation concerned with media reform. In its open letter to the FCC, it asks the government body to confirm that mobile wireless Internet access is subject to the same rules as traditional broadband Internet. The letter cites the FCC's Internet Policy Statement which states 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."

In Europe,  the Voice on the Net coalition, which includes Skype, as well as Microsoft and Intel, has asked the European Union to investigate the Skype policy. The Voice on the Net us is asking the EU to step in and enact policy that would protect consumers' rights to choose what applications they can use.

The matter is particularly acute in Germany where T-Mobile, Apple's wireless partner, has said that not only will it prohibit use of VoIP applications on its 3G network, it'll also restrict their use on the company's Wi-Fi hot spot network and cancel the contract of any customers who try to work around the restriction.

AT&T, Apple's partners in the US has been vigorously defending its policy. In an interview with USA Today, Jim Cicconi, AT&T's top public policy executive, said AT&T had "every right" not to promote the services of a wireless rival. "We absolutely expect our vendors not to facilitate the services of our competitors," he said.

"Skype is a competitor, just like Verizon or Sprint or T-Mobile," he added, Skype "has no obligation to market AT&T services. Why should the reverse be true?"

Meanwhile, Apple has remained mum on the matter, though it's easy to see why the company might not want to get involved. After all, being able to use VoIP over AT&T's 3G network could help Apple sell more iPhones by providing another attractive feature - but, at the same time, Apple doesn't want to risk alienating their business partner.

How the FCC and EU proceed could have far-reaching implications not just for the future of VoIP, but in terms of what restrictions mobile operators can legitimately put on the use of their networks, which also may have impact on peer-to-peer programs, live video, and other services.