When you purchase a cell phone it is likely be locked to that particular network provider. This means you can only use that provider's network.
Some service providers intentionally lock their mobile phone as a way of keeping their customers. These codes could be broken and there are many websites on the internet that can supply more info to them. All cell phones have characteristics that are hidden that are particular.You may visit http://fixt.ca/ to know more about unlocking cell phone.
Every cell phone has an IMEI- an International Mobile Equipment Identity number which connects its network and a telephone. This number is similar to a serial number.
The network is connected to the cell phone owner or subscriber by the IMEI. The SIM card also connects the phone to its owner along with the phone to the network.
Most of cell networks put a lock on the SIM card so that the cell phone can exclusively be combined making use of their service. So that you can change to a service that is new, you have to get a brand new phone having a brand new SIM.
If it still does not work after this, you may need to send the phone to a firm that offers the mobile phone.