The handling of calls within a specific PBX environment, typically the telephony system for a certain enterprise has been previously discussed, but there is one important issue remaining: how these calls will be charged? We need to have a consistent way of charging all calls between a customer’s IP phones, regardless of the actual phone number dialed (for instance, the customer may have phone numbers from different cities or countries).
When a call is made from account A (belonging to this customer) to account B (belonging to this same customer), PortaBilling will first look up the applicable rate not for the actual phone number, but for the special keyword VOICEONNETRX, and (if this rate available) use the price parameters defined by this rate to charge the call. When entering a rate to that destination in the tariff applied to your customers, you can specify how such calls are to be rated – should they be free calls, or charged a nominal amount, and so on. If there is no rate for VOICEONNETRX destination in the customer’s tariff, then the rate will be retrieved as usual, based on the actual dialed number
Using the VOICEONNETRX rate in tariffs allows you to avoid having "SIP-to-SIP" minutes mixed in with "off-net" minutes when products with volume discounts are used.
One associated feature is Ext-to-ext Distinctive Ring. When activated, for a call arriving from any IP phone within the same PBX environment PortaSIP will instruct the IP phone to use a ring pattern different from the default one (the phone must support distinctive ringing). This allows the end user to immediately recognize whether the call is coming from one of his co-workers, or from an external number.