Here in the state of Michigan, we had the first statewide 800 MHz, digitally trunked radio system in place that used the old Motorola ASTRO Platform 4.1 (3600 baud). When the 4th zone was completed in 2002, it was decided to upgrade to ASTRO 5.1 (9600 baud) to keep the system as current and up-to-date as possible. Likewise, this meant that Zones 5 and 6 would be built on the new 5.1 platform by Motorola.
The changeover from ASTRO 4.1 to 5.1 required extensive planning, and execution by the state radio technicians and support personnel from Motorola. This process took about a month to complete, but on selected nights at 4:00 a.m. the changeover took place. In the months leading up to the system switchover, all of the state agencies had their radios reprogrammed with menus that supported both the old and new templates.
This meant that if a Michigan State Trooper had to travel from Detroit up to Traverse City, he could maintain contact on old system until it was upgraded by manually changing the menu program on his radio. However, once the new ASTRO 5.1 system was firmly in place, he just left the radio in the new menu mode. Likewise, they still had their old 42 MHz VHF-Low band radios in their cars back then until the entire state was switched over to the new 800 MHz system.
The newer Motorola radios can be programmed to automatically switchover to the old system, especially when it can not locate one of the new 9600 baud data channels while roaming from one part of the state to another. With that said, there must be a systematic changeover plan in place for converting the old ASTRO 4.1 tower sites to the new ASTRO 7.9 platform. Here in Michigan they did it zone by zone, over a four week period. I am sure that OKWIN officials and Motorola have some sort of a changeover plan in place, complete with a weekly schedule.
73s
Ron