Wirelessly posted (htc Pocket PC: Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; IEMobile 8.12; MSIEMobile6.0) Sprint T7380)
I don't know anything about T-Mobile's IM system. Normally IM functions using data calls so on CDMA over 1x or EVDO data. They must have an app like Sprint's Picture Mail but the installed app for T-Mobile IM uses the SMS system instead of data. With email on CDMA your device also makes a data call over 1x or EVDO to connect to a server and download messages. On GSM I assumed that it is the same using EDGE or 3g data.
Personally, I recommend you use a Generic Rom that is not carrier specific. Then you can add stuff that you want. Vin, Sharkie, Energy and others make Generic Roms that are newer and more updated than Mighty.
You should check and see if your device has been HSPL Unlocked AND SIM Unlocked. For SIM Unlocked status just look at the radio version in red letters at boot. If the radio version is followed by WU then you are SIM Unlocked. If you see WF or something else then you're not.
To check HSPL status, enter bootloader by turning device completely off and then push and hold the volume down button then continue holding and press and hold the power button until the rainbow screen shows. If you see 1.00 Olinex then you are HSPL Unlocked.
Task29 basically wipes everything clean on your device except for the radio. It's done to eliminate corruption. Yes, before we had it many people would flash the shipped rom in between flashes.
Don't ever try to flash a GSM radio to your phone. You will have a brick. Flashing a GSM custom rom will cause a reboot loop.