The US Federal Communications Commission is seeking additional information about Apple's decision to reject Google's voice application for the iPhone in the United States.

Download the new Independent Premium app Sharing the full story, not just the headlines

The Google application is seen by some as a competitive threat to the voice services that come with the iPhone, which is carried exclusively in the United States by AT&T Inc.

The FCC sent letters of inquiry to Apple, Google and AT&T on Friday after Apple failed to approve the Google Voice app and removed a similar application from the App Store. Copies of the letters were posted on the FCC's Web site.

The commission said it was making the request in light of upcoming proceedings regarding wireless open access and handset exclusivity.

Last month, several US senators urged regulators to review exclusive handset arrangements between wireless carriers and cell phone makers and how they affect competition and choice in the marketplace.

President Barack Obama's choice to head the FCC has said he plans to review handset exclusivity arrangements.

An Apple spokesman declined to comment on the FCC move. Google and AT&T could not immediately be reached for comment.

Google said on Tuesday that Apple rejected its Google Voice app, a program that allows users to store transcripts of voicemail messages in their email inbox and find specific information within a phone message.

It can also be used to make low-priced international calls, and offers a single phone number that can route incoming calls to home, office and cell phones.

In addition, GV Mobile -- a third-party Google Voice iPhone app -- was removed from the App Store.

In its letter to Apple, the FCC asked for the reason behind the rejection and the decision to remove the third-party application. It also asked whether Apple acted alone or in consultation with AT&T, and what role AT&T plays in the approval process for iPhone apps.