CAR REMINDER and MOBILE MEMOS ARE the only iPhone apps that will playback your custom recorded message when you stop or leave your vehicle. It can also be used simply to record a message for later playback.
If youre planning the days errands record a message and turn on the remind feature and you wont be able to leave your car without listening to your recording. Of course you can disable the reminder at will and re-activate it at any time.
CAR REMINDER will playback your activated reminder from the background (requires iOS 4 or greater) or foreground. Just double click your home key to move any app to the foreground. The reminder has no limitation on the length of the message, or how many new messages you can create.
Continued use of GPS running in the background can dramatically decrease battery life.