Answer:

(Must have a Feature Pakage)HFAI means Hands-Free Answer Intercom. If your telephone has a HFAI button on it, you press the HFAI button and a green light comes on. When you are called over the intercom, the voice comes over the speaker and you can answer the call without lifting the handset.

The HFAI is only for intercom calls and not for outside calls. If you have Voice Announce Disable programmed onto your telephone, the HFAI feature will not work. Only one person can talk at a time. If two people talk at the same time, they cancel each other out.