All iPhone apps, including Phone.app, cause the radio to switch from "active" to "idle" mode when accessing the network far more often than traditional phones do. This causes the signaling channel, responsible for such functions as SMS messaging, initiating, maintaining, or ending a phone call, voicemail notifications, and DHCP requests, to become overloaded.
"This can lead to odd effects," the source told Ars. "For example, you could be in an area with perfect 5-bar reception, but because the signalling channel is overloaded your phone won't ring and calls go into voicemail." Our source also said that the iPhone was the first phone to cause this particular problem, but that Android and webOS phones have had a similar effect.
