Apple’s decision to disallow applications based on Google’s online telephony technology, Google Voice, from the iPhone has prompted an inquiry by the US’s communications regulator, the Federal Communications Commission.

Google Voice allows users to manage their telephone calls and answerphone messages, and to set up a single telephone number for all devices. The service is based on technology that Google acquired when it bought start-up Grand Central in 2007.

The revelation that Apple would not allow Google Voice and related applications on its App Store stirred controversy, and prompted influential technology blogger Michael Arrington of TechCrunch.com to publicly ‘quit’ the iPhone.

The FCC has sought an explanation of the decision, according to the Wall Street Times, and wants to know the extent to which AT&T, the iPhone’s sole carrier in the US, was involved in it.

Ironically, earlier this year the Federal Trade Commission launched a probe into whether Google CEO Eric Schmidt’s position on Apple’s board of directors breaks anti-trust laws.

“From my perspective, I don’t think Google sees Apple as a primary competitor,” Schmidt told reporters at the time, but he has also said that he is not involved in discussions surrounding the iPhone.

Not so long ago the quintessential object of desire, the iPhone – like the BlackBerry before it – is now beginning to attract less adoring press. A security flaw in the device’s operating system made the front page of the Metro newspaper last week, while reports of exploding iPhones have recently emerged in US media.