iPhone 4S 32GB compatibility

If you buy it factory unlocked from an Apple retail store you can use it with any GSM carrier in any country.

I purchased an iPhone 4S in the US from an Apple Store.  It is factory unlocked and this is clearly stated in the receipt they gave me.  I operate it in Spain normally with a sim card from Movistar.  All features and functionalitites work well.  You can also use it with an Orange or a Vodafone sim card but not all features are available.  For example, only Movistar provides visual voicemail.

Please note that Apple will only provide service under warranty in the country where the iPhone is purchased. The price of a factory unlocked phone from an Apple Store in the US and in Spain is not that different at current rates of exchange. 

Rojmer, many thanks for your comments. In fact, warranty coverage is an important issue to think about.

In any case, from what I have been searching, price levels are relevantly different: US = $299 (aprox. €245) vs. €599 in apple.com/es.

Do you know if in the website they publish final prices? (or if there are lots of additional taxes to be added).

Thanks once more!

You cannot buy an iphone 4s anywhere for $299.  That is the subsidised price for a phone that is locked to a carrier who requires you to pay for a two year contract on top of the $299.

The unlocked 32gb iPhone 4S in the US costs $749.

(I make that currently 17 euros MORE than your Spanish price)