1. Unless you have a restriction on your WiFi router it should use the WiFI first. some apps only go over Cell data so you need to do some testing by shutting off all but wifi in the connections options.
2 3G offers higher speeds. Same amount is charged to your account
3 yes . Connections but you will not be able to make or receive calls,
read here http://btsc.webapps.blackberry.com/b...0777&stateId=0