E.164 number formatting is a standardized numbering plan for the worldwide public switched telephone network (PSTN). It was developed so that associations around the world would have a standard format in which to express telephone numbers and is the primary standard that AVOXI uses. The format is the country code plus the number subtracting any preceding zeros.

E.164 formatted phone numbers are limited to a maximum of fifteen digits.  Below is a table with a few examples of numbers from different countries and their E.164 format.