Okay...it took me awhile to figure this out but I've got the solution and it's pretty simple; too simple in fact. It will not matter whether your devices are the Titan I or the Titan II; it's the exact same setup. If you are an AT&T user...your service comes directly from AT&T please use "AT&T". If your service is from Straight Talk with an AT&T network SIM card you will use "Consumer Cellular". They are a MVNO of AT&T. I realize there are many MVNOs that use the AT&T network but if you use Straight Talk, "Consumer Cellular" is what you want. Select it and close out. Go to Settings>>>About Phone>>>APN>>>every space is to be blank...no information...literally "blank". Close everything out, reboot your device. Once your screen is back to your Metro UI display return to Settings...and make sure everything under the APN remains blank and your mobile cellular data is on. MMS uses cellular data not wi-fi. Enjoy! I know it appears ridiculously simple...it is but not before I pulled my hair out doing it. Also remember is you're using Straight Talk or other MVNOs that will cut your service off the moment you're ten minutes late with the payment; please remember that; I fell for it the first time while troubleshooting and didn't do it again. For Titan I users...y'all know your devices can be interop/development unlocked ("rooted" in the Android universe), most of the custom ROMs include Straight Talk embedded within the HTC Connection Setup.