What does it meen to “unlock” a phone?

What does it meen to “unlock” a phone?
Answer #1
Certain phones are locked to Networks So you can only use those phones on like vodafone or T-Mobile
To unlock a phone means you can use it on any network
Answer #2
Unlocking your phone will allow you to use any Sim card from any service provider…
Answer #3
So many thanks bro
Answer #4
no or 1 sim ll work in locked cell. simple
Answer #5
For example If i have an Iphone or something I could use it on Virgin Moble or something
?
Answer #6
yeah so lets say you buy a iphone from t mobile and then decide to switch to virgin but still want to use the same iphone. You will have to unlock it so that it will accept the virgin sim card. Also locked phone have software limitations that some networks force, like can’t use mp3 as rintone as they want you to buy them.
Answer #7
ok thanks i got it now