lol very true. Mobiles can easily get wrecked if you get them slightly damp, and there'd be no come back on warrenty or anything cuase they've got moisture sensitive strips inside which change colour if they get too damp. So a condom would probably be good.
As for radio waves and things on that nature i guess you are putting it a little closer than it would normally be to organs and the such so maybe a margionally increased risk, but mobiles are under pretty stingent safy checking.
So i agree with Deia, probably not dangerous for you, but might be dangerous for your phone.
But main thing, i doubt they'd make very good toys really, the vibrate isn't that powerful on most, or variable puss they're not exactly the nicest shape to use as toys.
No phone activated toys, that's different