Cell phone in Spain

You don't say whether your phone is a GSM phone or not. If it is, and if it is unlocked, you can just buy a Spanish SIM once you are there. No need to do anything prior to your trip. If it is not a GSM phone it won't work in Europe. On my recent trip I bought an Orange SIM for 9 euro that had 9 euro credit on it, and a handful of local calls and three calls home to the US did not use it up.

Here's a link that explains a lot about various forms of communication in Europe and might answer your questions: http://blog.laptopmag.com/stay-connected-overseas-5-ways-to-save-money
You'll notice that it says that Verizon phones are not GSM which you will need in Spain. We purchased an economical phone kit online from Telestial before leaving the U.S. but if buying one when you arrive works better for you, we saw Orange stores everywhere.

It sounds like you know the phone works in Europe. If so, charge it up and make sure it turns on and keeps a charge for a reasonable amount of time. If not, recycle it and buy a new phone there, a new phone is probably cheaper than a replacement battery. The SIM card in it has probably been deactivated if it's been more than a year since you used it. When you get to Spain, pick up a new SIM card at any kiosk or phone store. If worse comes to worse, and it really doesn't work, you can always buy a phone cheaply there. I found two options for 25 euro, both included ten euro credit for calls.

I purchased mine through Vodaphone at El Corte Ingles (the store also carries Orange). Vodaphone is a competitor of Orange and, like Orange, they're all over. El Corte Ingles was the first place I looked. Since it was cheap, it didn't seem like there was much to gain by shopping around. I'm embarassed to say I let the phone get soaked in the rain. It died and I had to buy another phone at The Phone Store in Toledo. I found the same phone and another option for the same 25 euros I had paid in Barcelona.