CAN AN IPHONE BE BOUGHT AND USED WITHOUT A SIM CARD OR SERVICE?

Instead of shopping an iPod touch, i was meditative about shopping an iPhone 3g so i could make make use of of the camera. Can I make make use of of all on the iPhone on top of job and texting on the iPhone (music, games, camera, wifi) but a sim card? Also, what is the disproportion in between an iPhone 3g and an iPhone 3g s?