Billing Telephone Number (BTN) is the main telephone number that is associated with your account. All numbers associated with your account can be identified by your BTN. An account can also have multiple BTNs. Hence it is important to ensure the BTN you provide when porting a number to IXICA, is the correct one associated with that number. Unsure? Call your current carrier and find out. BTN is a requirement especially when porting from analog set of lines, PRI\\\'s, ISDN and other legacy services. NOTE: In the United States, a BTN may also be referred to as an ATN.