Had a stange problem happen twice in the past three days. While making a call via the contacts list with the headphones plugged in, instead of a dialing sound through the earpieces, the iPhone started vibrating instead. The vibrate switch was set to volume ring, there was no incoming call, and confirmed that there were no new visual voicemails or text messages. Finding this rather odd, I quickly ended my call and powered down the phone. After rebooting, the problem disappeared. Without the headphones, it would have been impossible to make a call, much less hold the vibrating phone up against my ear. Has anyone else had or heard about this?