I'm having the same exact problem with my phone. Among other things. Not only will it randomly start voice talk and driving mode by itself, but it will also say that there is a usb cable connected which drains the battery in a matter of hours. The phone will randomly crash and reboot by itself while using random applications. And about once every 1 or 2 weeks, the phone will get noticably hot while in sleep mode. I can feel the heat on my leg though my pocket. When this happens, the battery will drain itself in a couple hours. When I check to see what has been using the battery, it says the Android OS is using 90+% of the power.
I've had this phone for less than 3 months. I'm taking it back to the sprint store tomorrow morning since it's under warranty. I'm dreading it because dealing with these people is always difficult. If you find a solution to the problem, I'd really like to know.