I recently picked up an iphone for my wife (1st iphone) and had a question regarding the wifi. At home, I turn the wifi on since the internet service is much faster than the abysmal speeds I've been getting on Sprint's 3g network. My question is, do I have to turn the wifi off when leaving the house or will it just shut off automatically and revert to the 3g network? My concern is that if I don't turn the wifi off, it'll continuously search for a wifi signal when outside the house, presumably draining the battery. To the long-time iphone users: Do you toggle the wifi on and off when leaving the house? If you just leave it on all the time, do you notice a quicker battery drain? Thanks in advance.