I installed a used IVX 20+ for a client. It had worked fine previously. A few days after installation some of the phones would no longer ring on incoming calls, they make somewhat of a popping noise like they are trying to ring but not. I did find out that they were trying to set up a credit card reader and had plugged it into a couple of the system ports. Would that cause permanent damage? The programming in section 21 is correct and should cause the phones to ring as I want them to - x100-109 in ring 1, ring 3, VM AA 1 in ring 5.