Speaker Ringing While Talking

[m.filpo]

Hi,

We migrated from a nortel pbx and we are missing some features.
What should i do to make the Speaker Ring while in the phone.

Ex.
If A is talking, and B is calling A, them C, D, and all the persons around can hear the Ringing from A.

I think there is something similar if you use the headset, but i need that when using the handset

Thanks

Manuel F.