iPhone 3G call issues


I’ve had my iPhone 3G for about six weeks now and since the latest firmware update 2.1 I have a strange call issue.  The phone will ring, I’ll answer and the call will last about ten seconds before disconnecting.  It will continue happening for all calls: to correct the issue I have to turn off the iPhone and turn it back on.  Not just pressing the top power button to put the iPhone into sleep mode: actually powering it down.  Once powered back up everything returns to normal and continues to work properly for about ten days when the disconnected calls start again.  Let’s hope the next firmware update corrects this.