I’ve been spending the last few train rides to and from work every day trying to figure out how to tether my N900 to my laptop. While Firefox Mobile is nice, there are some things my desktop does better. I first tried using the PC Suite from Nokia, but that wasn’t successful (it apparently doesn’t support the N900). I then tried JoikuSpot, which is in beta. Sadly, I encountered the “phone reboots when clients connect” bug. However, if they fix that, that piece of software looks very promising. I finally went down the road to Bluetooth Networking.
In order to pull this off, you’ll need to get a handy little application from the Application Manager. Under the Network section, look for “Bluetooth Dial-Up Networking” in the Extras repository. After you install that, you will want to restart your device. Next, pair your N900 with you laptop (this varies per operating system. I used Windows 7 and these instructions will assume that). After pairing the device, add a new Dial-Up connection on that modem. The phone number will be *99# and you will leave the user name and password blank. Save the connection, but cancel it when it tries to dial (it will fail anyway). Now, launch the device manager, and find the Bluetooth modem that should have been installed when you paired the N900 to your computer. Open its properties, and go to the Advanced tab and set the Extra initialization commands to at+cgdcont=1,"IP","epc.tmobile.com". After this, you should be able to connect to the Internet though your phone.
To prove that it works, I wrote this on the train, and I’m posting while still on the train. :P
I found this particular wiki page to very useful in setting this up, but I found translating the instructions to Windows 7 to be a bit difficult at times.