Re-calling a now un-busy phone?

I have 3 phones tied to a certain extension. If someone calls that extension, all 3 phones will ring.

My problem is that if any of the phones are busy when the initial call is placed, that phone will not ring if it becomes free and the call is still ringing (on the other phones).

Example:

We have 3 phones: A, B & C.
We have 1 extension that rings A, B & C: 123
Phone A is currently in use.
Bob dials 123 and phones B & C begin to ring.
Phone A becomes available (ie - user hangs up) while B & C are still ringing.
Phone A does not begin ringing.

I suspect this is how it is designed, but the only way I can think of having A start ringing would be to re-place the call.

Are there any other alternatives that I should consider?

Thanks,
-S

Yes, siply enable…doh - whats the english word for it ?
Its the function to allow a second caller to “knock on” while talking.

Eg. SNOM: There you can set it to “visuell only”.

So whenever you finish your first call, the second is already present and signalled.

And yes, its designed that way:
When a phone is signalling “busy” to asterisk, a still ongoing ring would not be “re-routed” to the phone when free again.

Only chance:
A queue on these extensions with a very short roundtime:
That way, the call gets replaced and signalled on all 3 again after a short period of time.