I have a Motorola Motoroi XT720 that I bought in South Korea. My service provider is SK Telecom. When I insert my South African sim card (Service provider Vodacom, and using the phone while in South Africa) in to the phone, the phone simply states that it does not accept foreign SIM cards.
I want to change my phone so that I am able to use it in South Africa. I am absolutely clueless when it comes to rooting unlocking, but obviously eager to learn.
I can't really find any good resources, but after reading a lot of postings on various sites the general conclusion seems to be is that unlocking the phone directly is not possible, at least via "normal" methods. SK Telecom has altered the ROM such that you are not able to enter an unlock code no matter what you do; the functionality is simply disabled.
You can follow this XDA thread (or this one if that doesn't work) to root your device. Once rooted, you can install a custom ROM such as this popular one, just follow the instructions in that post. The new ROM should have an enabled unlock feature.
After that you need an unlock code. Sites that sell unlock codes are unfortunately very sketchy; I personally would not try one unless you can get a solid recommendation from someone you trust or know for sure has done it. You could attempt to contact SK Telecom and ask them for the unlock code, but they seem to be uncooperative from what I've read. Don't let them tell you that Motorola has the unlock code, since this is false.
