Worked it out... T-Mobile solution for Mac
OK - posting via BT dialup now, so guess this is working...
Downloaded the scripts from the link above (
http://www.versiontracker.com/dyn/moreinfo/macosx/13523) and installed according to included directions.
Networking System Preferneces, configure Bluetooth setup
Select PPP
leave all fields blank except for Telephone Number - here use 'internet2.voicestream.com'
Select PPP Options
Despite the directions from the download, under advanced options I've found you can leave 'Send PPP echo packets' and 'Use TCP Header compression' checked - they do speed things up a little bit
Under Proxies
Left all blank - didn't seem to need them
Under Bluetooth Modem
Used Sony Ericsson GPRS CID1
Checked all the boxes under (enable error correction, wait for dial tone)
Then opened up Internet Connect app and under Bluetooth hit 'connect'. Finally got online.
Seemed like I didn't have the right combo of letting the scripts do the dialing, including the Access Point Name (internet2.voicestream.com) and the right script. SO... for T-Mo that should do it.
Jason