"PS has anyone made one yet that is also a mobile phone?"
Yes. You can get a Pocket PC that functions as a mobile phone and there are also "Smartphones" that will run GPS software. Even if GPS is not integrated you can usually plug it in via a card slot or link via bluetooth (wireless).
My GPS is a bluetooth unit, a tiny little thing that runs for about 8 hours on a single charge. I usually put it in the top pocket of my rucksack and wear the pocket PC around my neck in a little waterproof case on a lanyard. With full mapping software you just glance at the screen and it shows you exactly where you are and where you've been. It shows grid coordinates in whatever style you choose and also height above sea level.
I know that you CAN do everything with a map and compass or by following walls or streams (I did it myself for many years), but that's like saying you can write a letter and post it rather than using the telephone.