Wirelessly posted (iPhone 3G: Mozilla/5.0 (iPhone; CPU iPhone OS 5_0_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A405 Safari/7534.48.3)
Assuming its a SIM-based iPhone, take out the SIM, give the contact points a clean and re-insert.
What is displayed on the screen (3G, E or O)?
Does it access data through wifi ok?