There is a continual battle between Motorola and the producers of reprogramming kits. These kits are part hardware and part software. The hardware is a cable that plugs into the parallel port on a computer and the data port on the phone. Different cable are used for the bag phone (the transportable and mobile models; i.e. not handheld. A black, silver, or grey box.), the Micro-Tac (a.k.a. DPC-550) series flip phone, and the (classic, ultra-classic, model 8000) brick phone. Software packages are available to program phones with a firmware version number less than 9122 and other packages for firmware later than 9122, including MPC, AMPS G2, MOT3.2, HTH-v2 and Motorola v.911 (HTH-V2 seems to be a clone of the Motorola program, but I prefer the original as HTH seems only to differ in that it thrashes the hard-drive around when loading and creates a directory called HTHRULEZ). An ESN transfer cable copies the ESN from one cell phone to another without the use of a computer.
The original motorola reprogramming software (version 6.6) seems to not take the speed of the computer being used into account, therefore the timing can be off with systems considerably slower or faster than that which it was intended for. Use a system with a clock speed of between 10 Mhz and 20 Mhz for best results. An 80386sx at 16 Mhz seems to work pretty well, for example. Also, try switching I/O cards if you are having trouble. Another problem is the supply voltage. Use exactly the right voltage from a power supply hefty enough to give the phone all the current it requires, 3 amps or more. If you are having 'low battery' troubles while programming, unplug the handset if that is appropriate, as it uses additional power for the lights, etc. Also, the NAM programming feature of v6.6 seems buggy, just program the phone from test mode.
Some phones with newer software versions would seem to require new programming software, however, switching the PROM with an older version works, and you can even switch the PROM back once the phone has been programmed.