We used our cell phones on our trip this summer. We had three families vacationing together, so there were five different cell phones between us. We were able to communicate well with the phones. We found only a few bad areas where we couldn't get a phone call through. We all got the plans with no roaming fees with the phones, so no difference in our bills after the trip.
We used walkie talkies on our trip the year before. They worked okay, but the constant sounds of other people on them bugged me and sometimes, we could not decipher if it was a person we were wanting to talk to or not.
If given a choice, I would stick with our cell phones. Our wireless company is Verizon.