Use the following steps to connect your Mac to the Internet via a Bluetooth connection with your Treo 650.
You will need:
1. A Bluetooth-enabled Mac with Mac OS X
2. A PalmOne Treo 650 smartphone
3. A subscription plan that allows GPRS connections.
If you have the unlocked GSM Treo you can skip the next step. If you have an operator-supplied Treo (from Verizon, Cingular or Sprint) you'll need to install the DUN Hack from Shadowmite.com.
If you're using Sprint or Cingular: Download the Generic GPRS and Generic 3G scripts from Ross Barkman's modem scripts site and install the files in /Library/Modem Scripts.
If you're on Verizon: Download and install Verizon BroadbandAccess Support 1.0 and enable the Verizon Support script using the same method Captnswing describes.
Then it's just a matter of pairing your phone to your Mac and configuring the Bluetooth Mobile Phone Set Up screens with the correct "APN," "username" and "password" parameters for your country and operator. Ross Barkman's excellent GPRS Info Page lists the appropriate GPRS parameters for most operators.
If you still need help, check out Trevor Harmon's Internet on Air.