What is the difference between teh Motorola DTR 550 and DTR 510 or the DTR 650 and DTR 610?
My understanding (but I have no solid evidence yet) is that there were originally the DTR410/510/610. They all had the non-removable stubby antennas.
The 550 and 650 were the next step up with removable and available longer antennas. Dunno what other differences there were, though. The x10 series were still all 900mhz so I would imagine they’re all still compatible with one another.
I’ve never seen firmware or CPS for anything other than the 410 in the x10 series.