Sorry, just some more clarifying questions to help someone answer your question.

I assume that you're talking about Israel, right? How popular are mobile phone carriers that use iDEN in Israel? As with most mobile phone technologies, it is often the quality and coverage of the network that makes the most difference in day-to-day performance, and not the actual technology.

When you say "mountains," I assume that you mean away from any cities/towns, like during hiking? And that probably also means away from most radio towers. That's going to be a challenge for any technology, if that's what you're thinking of.