<p>The microSim is a little chip inside the iPhone that tells it what phone company it works with. To get on the network of a different phone company, you pop out the microSim and pop in a new one. So with a new microSim from a Spanish phone company, all the calls in Spain would be local.</p>
<p>We did this when we were in Spain recently, and it worked pretty well, although we were never able to get text messages to work. There are apps you can use instead, but we didn’t bother.</p>
<p>The one we got came with 1 Gb of data and very cheap calls to the US (1.2 cents per minute or something like that), and it came with a US number that you could either forward your original number to or give out to your friends, so when people in the US called us they didn’t get charged for an international call.</p>
<p>All the plans seemed to be pay per call/pay per minute, when you run out of money you go into any phone store and add more money to it. Text messages were ridiculously expensive on the plan we had, so maybe it was good they didn’t work. The support people said “yeah text messages often don’t work to/from the US, sorry” but they neglected to tell us that when we got it. There are programs you can use instead, but they use internet data.</p>
<p>For a 4 month trip I might look for something with cheaper local calls and cheaper test messages. For a 10 day trip what we had worked very well.</p>
<p>Another option for the computer would be to get a tethering program that would allow the computer to use the phone for internet. This can chew a lot of data though…</p>
<p>Edited to add: for this to work, you will have to call your current cell phone company and have them unlock the phone. They will do this for no charge.</p>