Upgrade Jailbroken 3GS / Tmobile Data Network

[slcbdb]

I have a 3GS that is running 3.1.3 I jailbroke with jailbreakme.com and unlocked with ultrasn0w and run on TMobile. There are several apps that require 4.0 or higher that I would like to use and cannot. Is there a simple way to upgrade firmware without having to re-jailbreak and re-unlock? Also is there any way to access either the 3g or 4g network for data with TMobile yet?
Thanks for your response

[Neil001]

No, no , and no.... Each time you upgrade firmware(iOS) u upgrade you baseband ( bb ) so becareful. If unlock is important pay close attention to basaband, 3.1.3 is best suited for 3G,3GS, so if you're willing to give up a little perfection to go up to 4.x.x you may wanna check out snowbreeze 2.2.1. (window) Pwenage ( Mac ). Both of these Jb apps will preserve your baseband for ultrasnow unlock. You will need to create custom firmware with snowbreeze 2.2.1 google it follow instructions and you be fine