The easiest way to go about this is to talk to your network provide company and request them to unlock your phone. Call customer support service and ask them the key required for unlocking the phone. Tell them that you are heading for an international trip where you will have to use other cellular networks.
Sometimes people buy phones on e-bay which turn out to be locked. For that you will have to visit the office of the carrier provider company and explain your situation, talk to the manager if necessary. You will have to fill a few forms and convince them that you bought the phone online, and do not wish to use it on their network.
Apart from smart phones, all older phones can be unlocked pretty easily. All you need is a computer system with an internet connection and a data cable of the cell phone. Search for mobile unlocking softwares or code generators on Google. There are plenty of sites where keygens can be found for unlocking the cell phone. Download and install the keygen, and integrate it to generate mobile phone unlocking code. Put the code in the cell phone to unlock it.
Smart phones are not that easy. They require specific software and sometimes hardware to complete the process. For example to unlock a Motorola phone, you will have to open up the phone and drill into main circuits to use the phone in diagnostic mode. It is recommended to get this done by a professional, as the cell phone can be damaged permanently in the process.
Samsung phones require paid software, which are as expensive as the cell phone itself. So it’s best to hire the services of the unlocking service such as Travel Insider, which is relatively cheaper than those softwares.