... Do any recent mobile phones(cell phones/handphones) have a built-in radiation detecting device?

Because I would totally buy one. That would be brill.

I'm not the first to come up with this idea -- Cell phones could be used as radiation-detectors

Not just for terrorism, there ought to be plenty of other uses for the world out there.
Heck, we could even draw it near a banana for the fun of it.

Or use it as part of your research project for those scrumptious extra marks.
Mmmm... lunch..

This thought popped up into mind when I spotted the little 'DANGER, RADIATION AREA (WHEN IN OPERATION)' sign on the wall at the dentist.
It would've been awesome if I had a radiation detector on me at the time, I think the patient next door was getting some x-ray done(don't worry, it's safely secured).