What are the pro/cons of wifi versus 3G/4G ? I guess Wifi is a simpler hardware standard ? Or does 3g/4g enable more distance and mobility and allow towers to

What are the pro/cons of wifi versus 3G/4G ? I guess Wifi is a simpler hardware standard ? Or does 3g/4g enable more distance and mobility and allow towers to "connect" more terminals at the same time? I'm puzzled by wireless data layers as google had some wimax project in mind, but I've no clue how those technologies work. I can understand wired networks, but wireless seems like a mystery to me (I also wish there would be more open standards for long distance data channels).