Phone with additional line key on it

[VinceWhirlwind]

Here is a very simple question - and I hope there is a very simple answer.
 
I'm a senior executive and I frequently do radio interviews or take calls from senior politicians.
I have a Mitel handset that has an additional line key on it - my "private" line - what do I have to configure to tell the system that I (very obviously) require it to ring when I'm not on the phone, but don't ring if I am already on the phone?

[sarond]

Try changing Class of Service option "Force Device Busy If Any Line In Use" to yes.

[VinceWhirlwind]

Cool, let me test it...