"The one thing that's frustrated me more than anything else is that if they stick with the story of duplication, at what point are apps duplicating [Apple's functionality] on the iPhone? That's what eats at me."

Apple told the FCC that the reason it has not approved Google Voice was because the software "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."

"We put out four updates for VoiceCentral, and we were in there for three months and everyone was fine with that," Duerr said. "That's the piece of the puzzle that I don't see. What suddenly changed?"

When the three weeks ago, Duerr said he considered it a glimmer of hope. "We thought that the decision fell under the obligations of an AT&T and Apple agreement," he said, "and the FCC might shed some light on that and maybe make it go away. But now it's square on Apple's shoulders, and we're more frustrated than ever."

In its separate reply to the FCC, AT&T said that although it has at times notified Apple that some App Store submissions would violate the agreement between the two companies to ban Voice over Internet Protocol (VoIP) software from using AT&T's data network for phone calls, it played no part in the Google Voice situation.