My vote is for an i-Phone. Am waiting for my Verizon contract to expire to get one.
http://www.youtube.com/watch?v=56N7EsOZ5OUApparently you can now even make calls with an iPhone 4 with the Verizon network (I've heard that the iPhone was having some problems with the AT&T network). I don't think the iPhone has particularly good talk times or standby times and isn't very rugged for outdoor use and is extremely expensive i.e. upto 4-5x the ownership cost of other capable mobile smartphones.
Typcially an iPhone 4 will cost around £480 compared to £100 for a ruggedised Samsung B2710.
http://www.amazon.co.uk/Samsung-B2710-Makalu-Water-Mobile/dp/B0042ORU08The main advantage for the iPhone 4 is of course the ability for the end user to wave them around in the air with any embarrassment down the local pub, club and bar as an aid for social interaction.