I have four 947 phones and all of a sudden 2 different people can pick up the same line and hear each other as before a 2nd phone couldn't be on that line at the same time. Is the phone broke or is there a setting that needs to be reset?

SOURCE: At&T 984 Two people can pick up the same line

This is a feature for in-house conference calls. The problem lies with two people answering the phone very close together. In the handbook, it states that if you want another party in your office or home to join in on a conversation, push the Line button twice. This allows another individual in on the phone call. This also happens in our office. One party answers the phone, while someone else is trying to answer the phone. One of the two individuals inadvertently is the first one to answer and pushes the button 2x. This automatically lets the other individual in on the line. The solution is to make sure if you answer the phone, don't push the button 2x and assume someone has already answered it.

SOURCE: I have an MLS-12D phone that needs odd programming

Well, there is a lot of things to do.

First, here is how to do Auto Line Select.

Is it only 1 phone that should be making outgoing calls? Or is it not place any outgoing calls ONLY on line 3?

SOURCE: Intercom / page problem with AT&T phones model 944 and 955

I have the same setup in a small office I consult for and I found the intercom problem to be caused by the DSL filters. It seems the DSL filters also filter out the frequency that the phones use to communicate with each other. If any of the phones had a DSL filter on them the intercom and hold button would not work properly with the other phones in the system without filters. Once I took the filters off the intercom and Hold function worked fine.

SOURCE: phones will not release hold when picking up on a different phone

The filters are causing the problem. I ran into this same issue with a client. Once I removed the filter the hold function worked fine. It seems the DSL filter also filters out the frequency that the phones use to communicate with each other.

SOURCE: I've got an AT&T model

That beeping is letting you know know that the batteries are low or out. There's a compartment under the phone that holds four AA batteries. Open it and replace the batteries or put in fresh ones. The beeping will stop.