Using a iPhone in Spain

How long are you going to be in Spain? If it's only for a couple of weeks, your carrier should have an international plan that keeps costs down. Do you use your phone incessantly? Then maybe think about an international sim card or perhaps changing habits while you are abroad. This is a good link to help.
http://thebudgetmindedtraveler.com/iphone-abroad/

I like the local plan option when I go to Europe. It's much cheaper than anything my carrier ( AT&T) offers. Vodafone Espana offers a deal for tourists. 1Gb of data, 60 min calls worldwide for 15€ (VAT included). You can add 1 more Gb for 2€ more. Not sure how much extra for SMS messaging. I'm sure Movistar or the other providers have similar plans for travelers ( I'm a long time Vodafone customer)

It completely depends on how you intend to use your phone. Lots of calls, or lengthy calls to the States? Just want a phone in case of emergencies? How much data do you plan to use? Keep in mind that replacing the SIM changes the phone number (until you put your old SIM back) so that could be a consideration, too - or maybe not. If you can tell us more about how you want to use your phone, the length of your trip, etc., the better our answers can be for you.

We will be in Spain for 5 weeks. I would call home once a week. I would like to use phone for making a hotel reservation or restaurant reservation. Map guidance could be downloaded on iPad.
Possible email/text occasionally

Since your phone use will be minimal, just taking your carrier's international plan might be the simplest option for you. You can do email, etc., on wifi to save on data costs. Unless your Spanish is fluent, I suspect that you won't be making calls for reservations as often as you might think (unless you will be mostly in larger cities or tourist areas).

dixie,

I agree with Nancy. Check your home cell network first, as their international roaming plans may be the most cost effective method for light use. However, keep in mind that when travelling with your home number, you will be receiving calls from home and you will be paying for each one (be sure to tell all your contacts NOT to call you when on holidays). The best policy is to leave cellular data roaming "off" and just use Wi-Fi, as your data allotment will be much less than at home.

If your home network doesn't have good roaming plan, then you can start looking at buying local SIM cards. NOTE that your iPhone MUST be unlocked in order to use SIM's from other networks.

I just wanted to suggest that for times you are back in your hotel - or in a spot that has wifi, consider skype or google voice
as alternatives that you can use either from your computer, your iphone or other device.

As an aside, we also used our iphone - we have Verizon and they have various packages that you can purchase in advance or they can charge as you go which could be a lot more expensive. . Regardless of what you do with your iphone, be careful of data charges and roaming, etc. We opted for a Verizon plan - it was worth it to not have to worry about keeping track of minutes, texts, etc. Even so, back at the hotel we used skype.

Vodafone - 15 eurp for 1.2 gb data and 60 minute domestic spain, just used the sim on my recent trip