I have got a 3G contract plan of Vodafone (not T-Mobile, lol) here and it is quite fast enough to watch HD youtube. The problem is that I have only 1 SIM card and want to access the Internet using my laptop as well.
I came up with using Tethering Bot (http://graha.ms/androidproxy), which is a sock server daemon running on G1. I could do tethering via "adb forward" through USB cable, but the problem is that it is unstable (It kept disconnecting my IM clients all the time).
Today, I have found this article (http://www.gotontheinter.net/node/515) explaining how to setup Bluetooth PAN server on G1 and now I am able to forward all kind of requests through Bluetooth connection. Can't wait to have its next version, which is going to support DHCP.