I think it's to do with the traffic message storage thingywhatsit...
Basically if you leave your radio on a station that does traffic announcements, and TP is on, then when you leave your car, the radio will store up to 2 hours worth of announcements in it's memory.
When you return to your car, you press the TIM button (under the volume knob iirc) and it will play back any traffic messages it has stored.
Never used it, so I don't know if it works, but I'm pretty sure that's what it is.
If I'm wrong, then I'm sorry!
