Instead of paying for using your phone as a modem fee (usually 20), you can use your new treo as a modem and get on internet.
First you must have internet service on your phone such as vision for Sprint, and you must be in an area they provide this service.
Download PDAnet from http://mytreo.net/downloads/modules.php?name=Downloads&d_op=search&query=pdanet, you must install the program and sync it to your Treo.
Then go to your treo and launch PDAnet and simply tap connect; now you're on the internet.
Using the bluetooth feature might be little harder, you have to configure your hot sync program to the bluetooth port and change the setting in PDAnet.
With Treo 650 you can just connect the cable or select dial up networking feature in the bluetooth menu ( must have the newest update for your Treo) but I find it easier using PDAnet.