It used to be the case that unlocking a communications device could only be done by a service provider for a fairly hefty fee. Now, most devices can be unlocked for minimal cost with only the IMEI number from the device and a program that can be purchased for a nominal fee or even free from the Internet (or increasingly even the handset/service provider). Of course there are other methods as well as such as re-flashing the device with generic firmware. I've also seen Universal SIM card holders/convertors which may require trimming/cutting your SIM card which brings me to another point. One of the more interesting technologies that I've seen is a dual SIM card holder which can be used in your phone in order to provide you with the ability to be able to make/listen to multiple calls at the same time.
All this said, please ensure that your device supports the frequencies required by the network that you subsequently need/want to use.