Keep in mind the GRE PSR-800 is the only radio on the market today that can decipher Project 25 Phase II, TDMA.
I know a few systems are now using TDMA modulation. Philly is currently in the process of switching to a Project-25 Phase II TDMA capable trunked radio system, although they aren't using the TDMA yet they may someday.
It's a hardware issue, a simple firmware update will not allow radios on the market today to handle TDMA.
Realistic Pro-2022, RS Pro-197, Beltronics Pro500, Cobra 75 WX ST, PC78 Elite, PC68LTW