Apple has distanced itself from former ally Google by refusing to sell applications-based Google Voice internet telephony technology through its online App Store.
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The move signals growing rivalry between the two former allies, currently under investigation for violating US anti-trust laws.
The Federal Trade Commission is investigating whether Google and Apple are violating anti-trust laws by sharing two board members, according to the New York Times.
Google Voice would help business users of Apple's iPhone by enabling them to assign a single phone number to their mobile, desk and internet phones.
The move shows the disadvantages of Apple's exclusive approach and the growing number of areas in which Apple and Google compete, according to the Financial Times.
Apple has previously turned away internet telephony apps because they were too close to core functions offered by the iPhone.
But some analysts believe the ban on Google Voice may also be motivated by Apple's desire to protect its relationship with exclusive US iPhone service provider AT&T.
Google Voice offers users low-cost international calls over the internet, which could potentially reduce AT&T's US profits.