Should we buy sim card before arriving in Spain
 

We are planning a trip to Spain with 2 days in southern France. Should we buy an international Sim card before we arrive in Spain or just get a local Sim card when we get there? There's several different companies that offer them, but seems rather expensive. Does anyone know if local cards are a better deal? We have an IPhone with AT&T service and they said we could unlock the phone and get the SIM card in Spain. Help please

I've done it both ways, twice in advance and many times after arrival. I've always found the local ones much less expensive and work better. I'll likely never buy one in advance again.

Sometimes local cards are better deal, sometimes an international SIM, and sometimes AT&T with the international plan. All depends on the usage model in Spain for which OP has not described anything at all. Is data involved? If so how much MB? If you don't know, use the data counter. Is this just in case usage? Where are the calls - withing Spain, between "us", to US? Are calls bidirectional or mostly inbound or outbound? How much minutes are involved? Does it involve talking to someone who can make no calls less than 30 minutes in duration? Do you have to have a number before you leave? There are too many variables.
There is little reason to wait to have your phone unlocked. I can't think of any downside.

Indeed, Greg, very true, the variables are the thing. I use them primarily for utilitarian local calls, do my international communication mostly by email and data is of no concern to me. I use wifi when it's available free. Since the OP didn't specify I just advised based on my own experience which, as you point out, may not be applicable.

The answer is purchase one in Europe. Roaming fees are now capped: http://www.guardian.co.uk/technology...roaming-cut-eu
Just ensure the phone has enough money on it when leaving one country for another.