Mac Forums

ok so i am thinking about getting an iphone 4s and have a couple of questions:
(1) The iphone 4s has wifi but you can also search the internet without the wifi right? i think that is what the data plan thing allows it do, but i digress. anyway say that im in a place with wifi, will the phone use the wifi or will it use the data? like how does it know what to use?
(2) Battery life? good, okay, bad.