Hi Jay,
I'd miss my hat, gloves and waterproof jacket. I do like the idea of a phone / GPS in one unit. Unfortunately, my phone is my Blackberry that I use for work and couldn't replace it with a normal phone. While it has a GPS built in, it doesn't give me an OS grid reference. I'll either need to buy a second handset for walking or take out a personal mobile contract in addition to my office phone. (Which has some other appealing advantages.)
Mark