The simmering row between Apple and Google over the former’s rejection of an application for the iPhone reached new heights over the weekend as the US regulator gave an insight into the debate behind the scenes.

The spat started back in July when the FCC began looking into the application approval practices of mobile app stores. The regulatory body sent letters to Apple, AT&T (the exclusive carrier of the iPhone in the US), and Google asking about the rejection of the Google Voice for iPhone app.

The result is something of a ‘he said, he said’ argument, with Google claiming that Apple has outright rejected the Google Voice app, and Apple claiming that it is still reviewing the app.

In Apple’s initial response, which the company published in its entirety online, the company said: “Contrary to published reports, Apple has not rejected the Google Voice application, and continues to study it. 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 argues that the Google Voice application replaces native iPhone functionality such as Apple’s Visual Voicemail by routing calls through a separate Google Voice telephone number that stores any voicemail, preventing voicemail from being stored on the iPhone, effectively disabling Apple’s Visual Voicemail. Similarly, SMS text messages are managed through the Google hub, replacing the iPhone’s text messaging feature.

By way of response, Google has asked the FCC to publish its own response in its entirety, which the authority has done. In its letter, Google claims that it was informed that the Google Voice application had been rejected because “Apple believed it replaced the core dialler functionality of the iPhone.” Moreover, Google also claims that it was Phil Schiller, Apple’s senior VP of worldwide product marketing, who informed Google of the rejection in person.

The question now is, which firm is factually correct in its claims? Has the Google Voice app been outright rejected, or is Google able to tweak it so that it falls within Apple’s guidelines? This is likely to be something the FCC wants to find out too.

Coincidentally, Apple also rejected Google’s Latitude application for the iPhone, because it mimics core functionality supplied by the device’s pre-installed mapping application – Google Maps.