Certain apps won't work without a data plan (app world, google sync, etc), but for the most part you don't "need" a data plan with a blackberry. I know people that just use it for txting and a bit of surfing while at home on the couch.
WI-FI will work on any Blackberry, you have to change the settings.
1) turn on Wi-Fi under manage connections
2) go to Options
3) go to Advanced Options
4) go to Browser
5) Select Browser Configuration
6) Select Hotspot Browser
Now go to Wi-Fi follow the instructions and then your all set!
You will need the service book for WiFi for it to work. You usually get those service book entries when the device is activated. If it does not have it then call the carrier to see if they are able to push them to it.