I brought the tk102b with me on a (normal) trip last time and it lasted more than 4 days (mostly in idle mode), went on cars, buses, trains, hotels, convention halls etc, and mine didn't seem to have any problem regaining gps lock. I called it when it was in idle mode, it seemed to wake up, tried to establish gps lock.. and after 30 second or so without gps it would send a text with empty coordinate (was testing in hotel room); then I moved it near one of the windows, then it send me another text with the pinpoint coordinate. So I think that works out great for me, and a pretty smart way to keep in touch with you when you're trying to find the thing:
First text establishes that the unit is working, but you know it doesn't have gps signal. Second text was sent out as soon as it gets gps lock.
I have to say, though, that the TK102b is perfect for anyone who's already familiar with using unlocked phones with normal simcards, because it's just like a regular candy phone (Doesn't even need data plan if you don't plan on having it continuously stream the coordinates every few seconds\minutes). It's just like a cellphone; you plop the sim card in, make sure the sim is activated (can receive and send text) and you're in business.