The NEXTEL 800/900 iDEN TDMA system should continue running through 2010. In my market NEXTEL sites are still being built and the 800/900 footprint is expanding. You'll probably go through 2 or 3 phones before that network is gone. I carry the NEXTEL i-355, meets the mil stds for drop/water/salt fog, good battery life and off network comms if the system crashes (to another similar handset). Off net works about a mile in heavily treed suburban setting. Obviously only useful if you and your family/group have similarly equipped phones.

Try to verify coverage in your area prior to getting on anyones system, if you have a friend with a phone on the system you're thinking of switching to you can verify solid coverage where you spend most of your time. In my area Verizon has the best overall coverage but the worst customer service (ruins the hard work of the network folks), NEXTELs not too bad, T-MOB, Cingular, and Sprint are spotty but aggressivly building.