[StavrosK]

I'm not sure if the iPhone is sold locked here in Greece, but I would be surprised if it did; it would be the only one. You can get a subsidised phone with any carrier, and they don't lock it or otherwise restrict you. The basic view is "you promise to pay us X money per month, we give you a roughly X12[1] subsidy on your phone now". They don't even care what phone, if any, you decide to get with the subsidy.

Also, this happens every year. Once a year passes, you're eligible for a new subsidy of X12 euros.

[1] I'm not at all sure if the multiplier is as much as 12, but it's at least 6. The main point, anyway, is that they don't care what phone you get.