Each phone is a Dual Line phone. When the first call comes in it will ring the phone. When the second call comes in it will still ring the same phone. If you are already on a call, then it would display the second call and play call waiting tone. If no one picks then it goes to voice mail. When the 3rd call comes in it will go to voicemail after hitting the busy trigger.
Unfortunately there is no way to set the busy trigger to 1.
I think the confusion may be in where the call waiting is enabled. We do not support FXO lines with Call Waiting provisioned by the telco. We do not support hook flash signaling to the telco. FXO circuits should only be provisioned with caller ID by the telco.
If you are talking about call waiting being enabled on the phone that is a different scenario. In an example of this you might have two different FXO lines pointing to the hunt group. When you are on the phone with one line and a second call comes in you will be alerted on the phone by blinking LEDs and if no answer it rolls to the group voicemail.
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