I know this is out of date as far as a response to the original original question, but for those planning future Caminos here's what I did for our recently-completed (September 2013)
Camino Frances. While my wife and I both have Android-based smartphones, I also have an older unlocked basic phone which uses the GSM protocol, the same as used in the US by AT&T and Sprint, as well as the standard for Europe. I purchased a SIM card here in the States before we left from a company called Sims for Spain <
http://www.simsforspain.com/>. They offer SIMs for the Movil, Orange, and Vodaphone networks, the major networks in Spain. Their website explains the different plans available on each network. I chose the Orange network, and coverage on that network was excellent -- I can only recall one occasion where I didn't have coverage, and that was along one of those remote stretches in the mountains of eastern Galicia where we far away from a sizable city and away from a highway. Note that the Spanish SIM does not work in France, but since we were in France only a couple of days (SJPP to the border), it wasn't a concern for us.
This is not an endorsement of the company I purchased the SIM card from. For those outside of North America it may not be a viable solution. If you have an unlocked GSM phone, you can walk into any Movil, Orange, or Vodaphone store once you're in Spain and purchase a SIM there. You can also purchase an inexpensive phone there as well if you don't also have one. And there are other independent stores in the larger cities that are not tied to any particular network. The disadvantage of buying a SIM card after you arrive in Spain is that unless you spend a day or so in Madrid, Barcelona, or whatever your arrival city is, you'll have to wait until you get to Pamplona to get the card.
For internet and email, we used wifi on our smartphones. We were somewhat disappointed in the availability and reliability of wifi in most areas. I suspect the issue is range and bandwidth; i.e., too many people trying to use the system at once.
Jim