Why are mobile phones 'locked'?
Mobile handsets are sometimes 'locked' to the network from which the handset is purchased. This means the handset will usually only work when used with that particular provider.
If you want to switch to a different provider but keep your existing handset, you may need to get it unlocked.
You may also need to get your handset unlocked if you want to use a local SIM card in your handset when travelling abroad to avoid roaming charges.
You can find out whether your handset is locked by asking your mobile phone provider, or by trying a different network SIM card in it.
If you get a message that indicates there is a problem and you cannot make calls, it's possible that your phone may be locked.