Newbie here. A T-Mobile CSR sent me a doc that describes how to tether the Pearl to a laptop. It was missing a key step, which I found on another BB forum.
The extra step is:
Go to Control Panel - Phones and Modems - Modems - select the port your BB is using (usually COM4 or COM5; go to Control Panel - System - Hardware - Device Manager - scroll down to and click on Ports to see which ones are RIM ) - click Properties - Advanced - Extra initialization commands, then type (very precisely):
+cgdcont=1,,"wap.voicestream.com"
That worked for me. I'm using a Toshiba Tecra laptop running Windows XP Pro.
Sorry I've gotta run - I'll try to edit these directions later so they make more sense.