How NGN calls work
Ordinary phone calls
These are calls using geographic numbers starting with 01 and 02. When you make a call to someone else you use a traditional phone service. Whether you use your normal landline at home or your mobile phone, your call travels over the public network.
However, this may involve more than one telecommunications provider carrying your call. For example, if you're a BT customer and the person you're calling is with a cable phone company, both providers will carry the call. In this case, the call starts with BT (so they're the 'originating provider' or the 'call originator') and it ends with the cable company (the 'terminating provider' or 'call terminator').
Although you'll pay BT for your call, BT will then pass on a share of that charge to the cable company because they also carried the call for part of the way. BT will then keep the rest of the charge, which will include BT's profit for providing you with the service. This person-to-person call is known as a 'geographic' call because it was made to a specific location (for example, the home phone of the person you called).