So I just recently got an iPhone 3GS, jailbroken and unlocked on iOS 5.1.1 and got a plan with T-Mobile for a $30 monthly 4G plan, and I'm noticing iMessaging does not seem to work when sent to other people, but sending an iMessage to myself works just fine. I get a "Not Delivered" with a red exclamation point. I checked all my APN settings, they are all correct straight from T-Mobile's support site. MMS works as well with pictures. Has anybody else had this problem from being on T-Mobile? Maybe they are blocking iMessages from working? Any helpful replies would be appreciated, thanks.