Just prior to the official launch of the iPhone, T-Mobile issued a carrier update to enable LTE, improve battery performance and add Visual Voicemail support . The only problem is that some users were reporting slower speeds after the update. TmoNews reports that two well known cellular programmers, @joe012594 & @cooldayr2, have successfully modified the carrier update to “increase the amount of bandwidth allowing for better throughput of data and data connection.” That means you should be able to download apps quicker, browse the web faster and have a better overall experience on your T-Mobile iPhone after applying the patched carrier update.
Before and after speed comparison (via TmoNews):
The update does not require your iPhone to be jailbroken, preface by the coders and instructions for the hack are below. As always, please be sure to do a full backup of your iPhone prior to modding it in any way.