1 of 2 phones calling give busy tone

Hello People,

I’ve setup ringgroups so that if a person calls to no. 1800 also 1801 will ring.
But if a user is calling with 1801 Asterisk will look at 1800 and sees that phone is not busy and starts ringing.

So I want Asterisk to look at both phones, and if 1 of the phones is in a phonecall it should give a busy tone.

Is it possible to do this?

Help is very much appreciated.


Hendrik van der Ploeg
The Netherlands