Apple has responded to a request for information from the Federal Communications Commission (FCC) as to why the Google Voice application is not available for the iPhone.
The FCC said last month that it is investigating Apple's lack of support for Google Voice, amid allegations that the company is blocking it at the behest of AT&T, which sells the iPhone in the US.
Apple has denied this allegation, claiming that it is blocking Google Voice because it interferes with the iPhone user experience.
"Contrary to published reports, Apple has not rejected the Google Voice application and continues to study it," said the company.
"The application has not been approved because, as submitted for review, it appears to alter the iPhone's distinctive user experience by replacing the iPhone's core mobile telephone functionality and Apple user interface with its own user interface for telephone calls, text messaging and voicemail."
Apple suggested that Google Voice could be offered through the Safari browser but that, if installed as an application on the phone, it would interfere with key aspects of the phone's use.
The firm also said that it is concerned that Google stores all the information from Voice users on its servers, and had given Apple no assurances that the information will not be used in an inappropriate way.
Google said in its submission to the FCC (PDF) that, while Voice could be used via the browser, having it as an installed application is a superior way of using the service. Users could not, for example, access their iPhone address books using the web version.
However, the section of Google's response dealing with why it felt Apple had blocked the application was redacted and is not available for public consumption.
AT&T also issued a response to the FCC (PDF) in which it denied any role in the decision-making process over applications for the device.
"AT&T had no role in any decision by Apple to not accept the Google Voice application for inclusion in the Apple App Store," said James Cicconi, senior executive vice president of external and legislative affairs at AT&T.
"AT&T was not asked about the matter by Apple at any time, nor did it offer any view one way or the other. More broadly, AT&T does not own, operate or control the Apple App Store, and is not typically consulted regarding the approval or rejection of applications for the App Store or informed when an application is approved or rejected."
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