Brent Sordyl's blog

But here’s the fascinating point: the signaling issues aren’t just AT&T’s fault. In a quest to extend battery life on the iPhone, Apple did something ‘non-standard’ which compounds the issues – the iPhone constantly drops connections, going in to an idle state. Keepalives within the apps then reestablish a new connection after only a few seconds. Network equipment makers never anticipated this. Think of it as hanging up during a phone call when the line is silent, and then redialing to respond.
(Link: iPhone Design Causes AT&T Network Problems)