This is one of those ‘good to try, might be useful’ sort of things that I’ve been intending to try for some time.  First of all, a couple of caveats – some service providers don’t like you doing this, and almost all of them charge you extra for the privilege.  So, regard this as an emergency measure for use when all other connection methods aren’t available.

Or, like me, you decided to do it because ‘it might one day be useful’!

So, what’s tethering? It’s the ability to use the modem facility that the phone uses to communicate with the Internet to allow the computer to connect to the Internet via the phone.  In this post I’ll go through the steps I went through to connect my Vista laptop to the Internet via my Blackberry, using BT’s network.  As always – it worked for me, but don’t blame me if it all goes horribly wrong – proceed at your own risk!  You will need:

• A Blackberry with up to date software.
• A laptop running up to date Blackberry Desktop software. 
• A PC to Blackberry USB cable.

First of all, disconnect whatever network connection you currently have running on your PC.  This is most easily done by disconnecting teh network cable or turning off (or disconnecting) your WiFi connection.

Now, connect your Blackberry to the PC using the USB cable.  On your PC, run the ‘Blackberry Desktop’ program.  This bit is essential, and you can’t make use of the Blackberry’s modem unless the Desktop Manager program is running.

On the computer, open up Control Panel->Phone & Modem Options.  On the Modem tab you should see a new ‘Standard Modem’ added – on my PC it was listed as attaching to COM6, although COM11 is occasionally to be found.  Now go to Properties->Diagnostics->Query Modem and press the Query button – you should see a list of responses from the Blackberry.  The contents are not too important – the most important thing here is that you get something and it doesn’t pop up with ‘No Response’ or just leave a blank dialogue.

Now click Properties->Advanced and enter the following in to the initialisation command box:

+cgdcont=1,”IP”,”btmobile.bt.com”

The Blackberry Modem is now configured.  The next stage is to set up a Connection to the Internet.

Create a new Internet connection by Start->Connect To->Show all connections->Create a new connection.  Select ‘Connect to the Internet’ and then the ‘Set up my connection manually’ option, then next.  Then, select ‘Connect using a dial-up modem’ and Next, then give the connection a name such as “Blackberry Modem”, then Next.  Now, enter the following:

• Number :  *99#
• User name : bt
• Password : bt

And that’s that!  Save the connection and to test it just connect to the Internet using your newly created connection.  There are two things to note – in most circumstances it won’t be as fast as your normal WiFi / Broadband connection, and you almost certainly be charged by the volume of data that you transfer.  For example, BT’s rates are here.

If you want to try this on another network, this page may be useful.