I had this problems for 4-5 days on my network, signal problems selecting my network in Settings -> Carrier i have the message network lost, and people saying that they are trying to contact me but i cannot be always be found, that made me look for answers to my iphone problem, thinking that small price for this 3G model that i have was maybe too much, well, i did a firmware restore and install of Cydia, not puting all old application that i have, only Cycorder, Dtunes, Terminal, BossPref to see and test if the problems may be an application that i put recently and maybe one that wasn’t approved by Apple, well, that it the problem, haveing only those all’s great, no signal problem, and i did no restore from backup, which may also return me back to my problem, maybe, well Apple is doing a good job not allowing all application with bugs in Apple Store.