I don't know the rules by heart, but I'm pretty sure that after a period of time, something like 6 months, you can ask your operator here (I use Orange) to unlock the phone and they will. That doesn't disengage you from the 2 year contract you probably signed to get the iphone in the first place, but it at least allows you to put in other SIM's while traveling.

That part is easy. The hard part is dealing with the micro-sim in the iphone4. That's why I keep an iPhone3GS as my traveling phone.

But back to the OP, other countries in Europe, such as Belgium and Italy, require the operators to sell the phone unlocked. If I were you I would look for a used 3GS phone that is unlocked. It will be both cheaper and easier to use in Syria.