I own a BB Curve on the Rogers canada network and jmIRC works however I need to fiddle with APN settings several times before it worked.
at first i got a Tunnel Failed error, And then tried several APNs till i found one that worked. If you can't connect through a particular APN you'll usually get a DNS error, you could try calling your provider to see what APNs are available in your network.
goto your options > advanced options > tcp
APN = internet.com
user = wapuser1
pass = wap
I hope this helps some of you.