Tether your Vista desktop / laptop with a T-Mobile MDA Vario II

So while connecting to the super-fast 3G HSDPA data network on my T-mobile Vario II is great, I sometimes find that I want a full-size screen and keyboard to work with. I recently found myself without normal internet access on my Vista PC and decided to see if I could use my phone as a modem (which I used to do via Bluetooth with my earlier phone, the Sony Ericsson P910i). It seems that there are a number of different "how-to" approaches around, so this is the (definitive) approach that worked for me.

First, the scenario:
PC: 32-bit (x86) Vista Ultimate.
Phone: T-Mobile MDA Vario II
Connection type: USB (My phone battery lasts only half a day anyway, so it's nice to be able to connect without draining the battery)

Warning: you will need a working internet connection to download the bits needed to complete this connection!

Steps:

1. On your Vista PC, install the Windows Mobile Device Center. This step may well not be necessary, but I did install it and it works for me! I couldn't be bothered to uninstall and try without it, but you're welcome to try it. This download is at http://download.microsoft.com/download/c/f/2/cf2e986b-015a-4f0e-92ff-75f461f6e48e/drvupdate-x86.exe and will require you to validate your copy of Windows. Run through the install and set up your device as you want to. In fact, I think this step is totally superfluous (discussed later) but I don't want to omit it in case it isn't. I had originally thought the WMDC was included in Vista, but it isn't. It's a separate download, although if you hit Microsoft Update while your WM5 device is connected, MU should push this out to you.
   
2. Download and extract the USB modem drivers for your device to c:\ (or wherever). I got the driver from http://forum.xda-developers.com/showthread.php?t=288753 (Thanks Sergey123456!). This page also has the 64-bit driver, and if the 32-bit driver is anything to go by, it should work fine.
3. On your phone, Open up Programs -> Wireless Modem. Set connection type to USB and tap Menu-> Start
4. Connect the Vario to the PC with a USB cable
5. Vista will detect the new device "Generic Serial" and try to set it up. It will fail. So when it gives up and asks you what to do, point it to c:\USB_MODEM_VISTA\USB_MODEM_VISTA\USBMDM.INF
6. It should then go and install the drivers and you should now have an entry in Device Manager under Modems called HTC USB Modem.
7. Right-click the entry for the HTC USM Modem and go to the Advanced tab. In the Extra initialization commands field, type in the follwing: at+cgdcont=1,"IP","general.t-mobile.uk"
8. For some reason, my Extra initialization commands field was disabled when I first tried this, but after clicking around a bit and opening the modem properties again, it was enabled. Yipee.
9. Save these settings and head to the annoying Network & Sharing Center.
   
10. On the left pane, click Set up a connection or network.
11. Choose set up a dial-up connection.
12. Assuming you only have one dial-up modem in your system, it will then ask your for details. If you have more than one modem, it'll probably ask you to choose which one you want to use!
13. Enter *99# for the phone number, and leave the username & password fields blank.
14. Hit Connect. (I wish they would just let you create a connection without forcing you to try to connect immediately).
15. Cancel the connection if it's trying to connect.
16. On your phone, without stopping or quitting the wireless modem app, click the 3G icon in the status bar and make sure you are not currently connected (otherwise the phone will scream at you to "Please end data call first" !!).
17. On the PC, double-click the connection you just created to connect. I would go into connection properties and un-check the "Prompt for phone number" and "Prompt for username" boxes so that it connects without hassling me any more.
18. That's it!! You should be online! If you're not, then... try Google.

Mine usually shows a connection speed of 230kbps, which is nowhere near the 1.8mbps I have seen in broadband speed tests from my phone directly, but I'm writing this post via that connection and it's pretty usable!