If someone calls me while I am talking on the phone, they do not hear a busy signal

This is completely normal and is due to the fact that most adapters by default have the "Call Waiting" (CW) feature activated.

See the setup guides for how to turn off the CW and to signal busy.

Hilfethema HT040052. Herausgegeben Donnerstag, 26. August 2004. Aktualisiert Mittwoch, 16. Februar 2022.