This answer applies to the Panther version of Mac OSX. Go to System Prefs-->Network-->Location-->New Location.
I called my New Location "Cingular Wireless" without the quotes.
Then select your new location and next to Show select Bluetooth. Under TCP/IP next to Configure IPv4: select Using PPP. Leave the DNS Servers and Search Domains boxes blank.
On the PPP tab for Service Provider type "Wireless Modem". Account Name is WAP@CINGULARGPRS.COM and Password is CINGULAR1. Make sure you have everything capitalized the same. For Telephone Number you need to enter "WAP.CINGULAR". Leave Alternate Number blank. Select Save password.
Go to PPP Options. I have nothing in Advanced Options checked, and under Session Options I have unchecked "Connect automatically when needed" and "Prompt every..".
Now go to your Bluetooth Modem tab. Uncheck "Enable error..". Under the Modem, you need to select a script that actually doesn't come with your Mac. You need to download it from here - www.taniwha.org.uk/. At that website, scroll down to your kind of phone, and then select the appropriate file to download. Since I have a Nokia 3600 with GPRS, I selected this one-> »www.taniwha.org.uk/files ··· 4-05.sit
After downloading the appropriate file for your phone, read the "Read Me First" file located in the archive. Place the script that you want to use into
The following link directs you to a page that shows you what GPRS settings you should use on your phone. If you cannot already access GPRS internet from your cell phone, you need to be able to do this before trying to use your phone as a modem. »www.taniwha.org.uk/gprs.html
Now open Internet Connect and go to the Bluetooth tab. You can find Internet Connect in the Applications folder. Add a new Configuration and call it "WirelessModem". For telephone number use WAP.CINGULAR, and for Account Name use WAP@CINGULARGPRS.COM, and for password use CINGULAR1.
Under Modem select the Script you chose in Network Preferences.
That should do it. I chose to display the Modem status in the menu bar so I can just click it and click Connect from there, but if you don't want it displayed in the menu bar, you can click Connect from Internet Connect-->Bluetooth. When I click Connect, I get a prompt on my phone to accept the connection. I choose Yes, and it all runs smoothly.
Also, if you are using Cingular, it is best to add the $19.99/mo package to your plan that provides 1500 text messages, 200 e-mails, and most importantly unlimited wireless internet.