I am traveling with an iPhone 4S and an iPad mini. I will leave discussions of why/why not and pros/cons to other threads. Suffice it to say that being able to be reached in near real-time was a nonnegotiable condition of being able to walk the Camino for me.
After considerable research on this forum and other locations, I ended up getting a local Spanish SIM card in Pamplona for both. My home carrier in the US is Verizon so I had to request that they unlock the phone before I left, and they agreed without any issues. I have been a customer with them for over a decade so not sure if they would be so cooperative if one were a more recent customer with them. The iPad is by definition unlocked but you need to know which version of carrier type it supports.
For both SIM cards I paid about 10 euros each initially for a month-to-month voice plus 3G data plan. Spain does not yet have 4G service and the 3G data service is not particularly fast, but I have had coverage everywhere along the Camino except one night purposely out of range in the mountains (Manjarin).
For the SIM card on the iPad I had to top-up with about 20 euros in Burgos in order to buy more data but otherwise no additional charges. I don't use the 3G data for uploading photos and such but otherwise I have not done anything special to manage my data usage.
For the SIM card on the iPhone I have topped up several times, probably spending about 50 euros total. The data usage has never been an issue but I have non-trivial volume of text messages and international voice calls, maybe 20 texts and 2 hours of international calling a week.
Retrospectively I think I could have stayed on my home Verizon plan / SIM card and just paid their international plan, and probably ended up paying about the same amount for the iPhone. I will say that there has been an unexpected benefit from using the Spanish SIM which is that my normal USA cell number does not reach me and so the volume of calls received has been reduced to the truly-essential from the small # of people who have the Spanish number.
With the iPad, I have been glad to have the 3G data service. While WiFi is theoretically available almost everywhere, I have found it often not working, or very slow, or unreliable. It's just a lot less hassle to have 3G so I can check in when I need to instead of having my daily routine oriented around WiFi access. If having Internet access is important at all then I would argue that using 3G cellular data instead of WiFi is actually more liberating along the Camino.
There is no question that if one could travel the Camino without any devices or connectivity, it would be a better experience. For me such a restriction would have meant that my Camino would have been no experience at all. So I made the tradeoff and frankly have not thought it much of a big deal. Both devices have off buttons and ultimately learning how to manage one's own control over the metaphorical off button of life is a key lesson of the Camino.
Buen Camino.
