For some reason, when I dial extensions 800 on our Cisco SPA50x phones, it doesn't actually dial but instead initiates a company wide intercom (i.e. like *9 + <ext>) across all of the Cisco SPA50x phones in our company. We are using firmware revision 7.8.9c currently, but it also works with 7.4.8a and 7.4.9a. I'm trying to figure out if this is an undocumented feature of 3CX or something to do with the phones. I discovered it by accident while trying to assign extensions 800 to an IVR. Anyways, the feature works AWESOME! The audio initiates instantly, has little or no delay and doesn't interrupt a telephone call if you have multi-call capabilities turned on in 3CX.