Mobile solutions for a small office

I am looking at the best mobile technology for a small one office practice with about 10 staff, most of whom are out and about a lot of the time. Do we go for smartphones, iPhones, notebooks or laptops with 3G dongles - I'm not sure what the best way to go is. The wrong choice looks like it could be expensive, and would tie me in to a long contract so I'd be stuck. Anyone got any suggestions?
Nigel Harris