i have an 8320 and am logged onto the jivetalk app was we type via my home wi-fi connection. works perfectly. i downloaded the trial from the website but later proceeded to purchasing it for $20 anyway. from my knowledge, jivetalk is the only blackberry messenger so far that supports wi-fi and will work without a data plan.
i don't know if the settings are much different, but what i had to do was just:
open beejive/jivetalk > go to preferences > scroll down to networking and there should be a "wifi option" bar. at default, it is set to "mobile network preferred" which you simply switch to "wifi preferred". you should be able to log on with no problems now. (well, i've only used msn & gtalk so far.) hope it works for you.
opera mini works with me, too. didn't have to fix anything after the download.
off topic: i still can't figure out how to use the
facebook app with wifi though. any ideas?