Allegan County still uses an exclusive ProVoice system. Ingham, I think still has a couple ProVoice TG's (unknown if encrypted) but can't confirm. But for SE MI, save your money.
RR database says Consumer's Energy might have a couple ProVoice TG's too, but I can't confirm that either.
This ProVoice upgrade would have been cool 10-15 years ago when Livonia was still on an EDACS system with ProVoice TGs. Livonia has replaced that system with an encrypted P25 sys.