I've wondered what happened to SMR. Dozens of 5-frequency systems just disappeared overnight here in Birmingham. All that's left is a few UHF LTR systems. Ambulances, businesses, utilities - all SouthernLINC or NEXTEL.
There is no mandate. Here in Jefferson / ST.Clair County Turbo is rapidly being adopted by small departments & even one County is going 100% Turbo for Volunteer Fire. Yes, most "modern" radios can be programmed for narrowband but you have to remember that there's more to it than that. Many agencies in this area have aging repeaters & dispatch consoles. Also, going narrowband analog means a reduction in coverage, sometimes by almost 25%. From what I understand (I'm just a hobbyist) the Vocoder Turbo uses has an advantage over P25 and Turbo systems are supposedly cheaper. Now we wait for a Turbo scanner or something less buggy than DSD.