I use a HTC Touch Pro HD as a phone, Sat Nav and PDA all in one.
Excellent phone, decent 5Mp camera, price tag made the eyes pop but you only live once!
When there's no cell available, as it's a 3G phone, it goes absolutely birko trying to get a service and promptly deadens the battery in its attempts to reconnect to the network. Thankfully it has a mode where the phone can be turned off independently of bluetooth, WiFi and the GPS.
I've looked at satellite phones. If I had a rural address I might go for one, but without the subsidy, they're just stupidly priced. What I'd really prefer (given a rural address) is a satellite internet connection and VOIP phone. Shove that in the 'van and then I could google the restaurant's phone number just south of Broome as I head across the top end and book a table for me and the missus!
Cheers
Tony