In plain English
A mobile phone line is the service connection used for mobile service. Activating it means switching that line from not having service to having service.
In context
Here, "activate line" names the action of starting service on the mobile phone line.
- Situation
- Porting numbers, activating SIM or eSIM, replacing devices, and changing account details
- What it communicates
- labels the action to start service for the line
Meaning limits
By itself, the term does not say whether that action is allowed, successful, or already completed.
Examples
“She kept the same phone but had to activate the line again after a month without service.”
“At the counter, the clerk will activate the line while the customer chooses a case.”