Hi, We have a 3cx V15.5 SP2 pbx and use a grandstream HT701 for our intercom and front door. But we have rather annoying issue. Our frontdoor triggers a call (just 1 ring) every half hour. In the past we learned to live with it but now we need to address this. Because we now have the ability to call extensions with our mobile phone. And now the cell phone rings every half hour due to that doorbell. Thanks for the help!