Originally Posted by dlx
...need more info.
Did you recently upgrade to 3.1.2?
Are you jailbroken? How did you jailbreak?
Has it been doing this recently or for a while?
Did you recently install/uninstall something?
Have you been having any other service provider issues (frequent dropped calls, not receiving voicemail/texts, push breaks, data drops, etc.)?
Here are some possible answers with what you have given us:
The tower in your area has bad routing services (or router). (You'll have to wait for your provider to repair the issue.)
You have a bum antenna. (iPhone will need to be replaced/serviced.)
Something related to your restore or jailbreak went haywire. (Do a clean restore and jailbreak.)
Something you installed/uninstalled screwed up some key network settting. (Do a Reset Network Settings.)
We really need more info to go on to help you, though.