I am a user at another iPhone site and it seems that when I really have questions, there is nobody there to offer advice or help for a few hours or days. My question is this: I have a factory unlocked iPhone 4 running iOS5 with a modem firmware of 04.11.08. I am considering jailbreaking since I cannot get any MMS messages on T-Mobile through this phone on this iOS. I don't know if it's the iOS or my carrier but I do miss being able to completely customize the phone to my liking. Is this possible? Can I downgrade and jailbreak it untethered? Or should I just stick with what I have. All thoughts are appreciated.

Also, if you think jailbreaking is a good option for me, please offer some help on what to do. Kind of new to all of this.

While Apple is still signing iOS 4.3.5 - you should be able to downgrade both OS and baseband. However once iOS5 is released it will be impossible to downgrade.

I would advise you to save your 4.3.5 SHSH blob now via TinyUmbrella

As an unsupported carrier, it seems that t-mobile requires some commcenter patching to allow you to load a customised carrier bundle that properly sets the t-mobile carrier settings. This requires jailbreak.

nice information....