Okay so im going to use this guide here How to Jailbreak 4.0 iPhone 3G/iPod Touch 2g on OS X/Windows to upgrade but before I do I want to know a few things.

Im running a iPhone 3G on 3.1.3 (7E18) Im on T-mobile and want to know if it will lock the phone again. Also, it took me forever to figure out MMS on the phone and I dont want to lose that will I? I have multiple apps that I dont want to lose so basically I want to know if upgrading changes anything on the phone or locks it.

Thanks for the help. Sorry for the noobish thread but just want to make sure and ive never done it before.