Simple terms. what does it mean to unlock a cell phone

[tremmor]

And why would ya?
A family member is overseas with a 4G android.
I comment i didn't think he could get a signal to call.
He said something about unlocking and using as a 3G.
whats that mean. He's paying for it. im confused about this.

 

[johnb35]

Unlocking a phone usually means you can use it with any carrier. I'm sure there are issues with some phones though.

https://www.google.com/search?sourc...1T4GUEA_enUS429US429&q=unlocking+a+cell+phone

 

[tremmor]

He said the same thing. To use another carrier.
thanks