This is a brilliant idea from LG, The LG Decoy

LG has come up with a new phone, which is an outcome of a brilliant idea. Yes, as the name suggests, it has an integrated bluetooth headset that fits discretely into the phone when not in use. So you dont need to search for the headset when the phone is ringing. Just pick up the phone, unlock the headset, talk and then place it back in the phone. It also charges automatically when locked into the phone.

Check it out - LG Decoy Website