EDIT: This no longer works. If you have the package installed, I would recommend uninstalling it.
I’ve talked about how it works here. In short, I’ve made a proxy server that adds the string “tmobile” to all URL requests on the iPhone because T-Mobile allows internet access to URLs with “tmobile” in it. You can download the deb and install it manually from here. You can also add the repo /cydia/ to Cydia. This script works for any unlocked iPhone running T-Mobile including prepaid phones. However, I’m not responsible if you abuse this and get charged. Let’s start the countdown. I predict T-Mobile will have this bug fixed in a month.
Please note that it’s only tested and working on one phone. So it’s pretty beta-ish. If it doesn’t work, please post as much info as you can in the comments, so I can fix it up.
Also, I noticed that it doesn’t work on the internet3.voicestream.com APN. I use wap.voicestream.com and it works there. Another thing that breaks this is any “T-Zones $5.99 hack” (which hasn’t worked for a while now) is installed. The problem is that if you already have a proxy set for ip1 (EDGE/3G) interface, then this won’t work. You can’t modify EDGE/3G proxy information from Preferences.app, so if you manually edited your proxy information in preferences.plist, installed a package that did, or installed a mobile config that did revert the changes to use this.
If all else fails, install my configuration profile by going to /cydia/install.mobileconfig from your iPhone and install that configuration profile. It will set the APN and proxy for you.