I have been having a weird problem with my iPhone. About 2-3 months into getting it since launch about 75% of my incoming calls go directly to voicemail on the first attempt. When the person hangs up and calls back it rings fine and I can pick up and talk. It doesnt matter if the other party is landline or wireless. The phone is only jailbroken for installer.app Not sim unlocked and activated via ATT/iTunes.

Any ideas/thoughts are much appricated.