There are plenty of GPS mapping applications available on the smartphone market. Many of them will easily beat any modern standalone solution in terms of usability, convenience and features, even without data connection available. The problem with them is the smart phone itself. It has limited battery life, not rugged enough, its GPS antenna is tiny, and it is prone to software crashes and weird glitches.

It is possible to overcome most of that by selecting a good field smart phone in the first place. Forget the iPhone. Get Android. My personal choice is Motorola Razr Maxx on Verizon network ( just as an example of a good choice: large battery, OLED screen, rugged case). Then add Otterbox Defender case, buy a decent external battery with USB port (and perhaps a solar panel), refrain from "playing with apps" on your phone (or at least be observant for "bad" applications and make backups often). To overcome weak antenna issues - get an external BT GPS receiver module (e.g. Holux, providing 20 hr of battery time).