When you call a mobile phone and get a message saying "the line is busy," it means that the person you are trying to reach is currently on another call [1]. This could be because they are talking to someone else, their phone is off, or they are in an area with poor reception.

Possible reasons for getting a "line is busy" message:

1. The person you are calling is currently engaged in another conversation.
2. The person's phone is turned off or in airplane mode, which prevents incoming calls.
3. The person's phone is out of network coverage or in an area with poor reception, making it difficult to establish a call.
4. The person may have activated call forwarding or call waiting, which can result in a busy signal if they are already on a call or have set specific call forwarding rules.

If you encounter a busy signal when calling someone, you can try the following:

1. Wait a few minutes and try calling again to see if the line becomes available.
2. Send a text message or try reaching out through another communication method.
3. If it's an urgent matter, you can try contacting the person through an alternative phone number or reaching out to them through a different contact.

Learn more:

1. What does it mean when you ring a mobile and you get this ...
2. Why is my iPhone saying user busy when people call me?
3. IP phone all lines busy when active call - Cisco Community