AH!!! I can go light another fatty straight away without any worry for my brain! I just found this on Wikipeda (so you know it HAS to be true):
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"Funding for communications upgrades from the Department of Homeland Security usually requires migrating to APCO-25."
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Giving an interesting nod to Woody's question about durability, I also found this line on the page in a section that was comparing and contrasting various systems ...
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"And while Terrestrial Trunked Radio systems are sometimes cheaper - handsets are often not suited to more rugged environments."
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I realize, of course, that we were talking about MOTOTRBO and not TETRA systems, but I found it interesting that durability is an issue with other non-P25 systems (now that I write this I'm suddenly confused about what the operating system [MOTOTRBO vs. TETRA vs. P25] would have to do with the durability of the hardware into which it is placed. Maybe I'll think more about this after the smoke clears. I suddenly have the munches.).
http://en.wikipedia.org/wiki/Project_25