Unlocking Iphone to use different sim card?

Hi. I was going to travel to Spain so I want to unlock my Iphone so I can use a different sim card. I was wondering how I would do this process and what are some of the advantages/disadvantages to unlocking the Iphone 4.

Well that's the biggest advantage that the phone can take any carrier around the world. You are the one to decide what carrier and plan you want. Unlocking also brings phone value up. There are really no major negative side affects.

To unlock an iPhone the remote unlock service would be a better option because, you need not give your mobile to someone else nor do you have any chance to enter the wrong unlock codes. Regarding the advantage in unlocking an iPhone 4, once unlocked you can switch to your desired network hence even if you travel borders you can change the sim to PAYG of that country thereby cutting down the roaming cost. As far as I know there's no disadvantage if you get a proper legal unlocking service. To get such an unlocking service for your iPhone 4 you can approach http://www.prounlocking.com/apple-iphone-4/rs16wp9/ and by submitting the country and network to which the mobile is locked to you will be able to remove the restriction from the respective network. This will be a permanent unlocking solution. Once unlocked you can use the mobile with Spain GSM network.