My friend's mobile phone can send text messages and videos every day, which means I keep talking every time I call. What is the reason?

The mobile phone number is blacklisted.

Usually, when someone on the blacklist calls you, there will be no call reminder on your phone and no information will be displayed in the call record, but the caller will receive the following prompt: the phone you dialed is power off, sorry, the phone you dialed cannot be connected for the time being. It should be noted that short messages can still be sent, but there is no read prompt for the short message function at present. Some mobile phones will not be reminded after receiving the information sent by blacklisted phone numbers, but will only appear in the block list.