I hope you mean a G4 Mini
Some people use 3.5" drives, but as you pointed out they made to sit on nice stable desks and not be bounced around a lot. I would suggest the extra money to get a 2.5" drive to be sure.
BluePhoneElite 2 (still in beta) lets you use handsfree with a compatible cell phone. There has been a thread or two in this forum about it.
-dave