Brian has a great way to use a T-Mobile Dash as a high speed connection using Parallels under Mac OS X –
I have almost no complaints about the T-Mobile Dash. It’s small, it’s fun to use, and T-Mobile’s data plans are cheap ($30 for unlimited EDGE+T-Mobile Hotspot). But it’s got one annoying flaw: instead of Bluetooth Dialup Networking (DUN), the Dash uses Bluetooth LAN Access (kind of like a Wi-Fi access point, but for Bluetooth). For some reason, Mac OS X Tiger doesn’t support this part of the Bluetooth standard (there are reports that earlier versions of Mac OS X could support this through the Bluetooth Serial Utility, but that’s no longer part of Mac OS X, and I had no luck running the Panther version of the Bluetooth Serial Utility on my Intel Mac).
Sharing the Internet connection over USB is out of the question too. As best I can tell, the Mac expects USB networking devices to use something called CDC, but the Dash uses a Microsoft-specific protocol called RNDIS (I’m pretty sure I fumbled that explanation, so feel free to add more information in the comments). People who have gotten their hands on the unreleased updated to Windows Mobile 5 (called AKU 3.3) have reported that the devices work correctly with Mac OS X. But until that’s released, you’ll need a tricky hack to get this to work.
HOW TO – Tether your Mac and T-Mobile Dash with Parallels – Link.