I work in a Telecom company and we have several kins of telephone numbers.
WTN - Working Telephone Number
BTN - Billing Telephone Number
ATN - Account Telephone Number
My understanding is that WTNs roll-up into BTNs. That is to say that several Working Telephone Numbers can be grouped under a single Billing Telephone number.
But how do ATN’s play into this? Do BTN’s roll-up into ATNs?