If you take out a mobile phone or tablet with 4g connectivity on a contract, then 9 out of 10 times the providing company will have a network lock on the device; This is to keep you tied in with them and their services. Usually after around 6 months into the contract you can request for an unlock code at a chargeable price through that particular network. If you have bought a phone from a friend or off a website, you void this option and cannot request the network to unlock your device.
So to be able to use your locked phone with other network carrier's, you are required to unlock the phone with a code which can be straight forward if you go to the right place.
This is the reason why it is important to approach a professional to unlock your phone, so that you can use the network provider that has a plan package to best suit you. We can unlock all makes and models of phone's, however timescales of how quickly they can be unlocked will depend on the model of handset and network which it is locked to.
Another benefit of unlocking your device is if you are visiting another country, you can use a local sim card to avoid expensive roaming charges.