Which of the following is true about E.164 telephone numbers?

E.164 telephone numbers are governed by international standards that define the structure of phone numbers used in the public switched telephone network. One of the critical characteristics of E.164 numbers is that they must always include a country code. This country code is crucial because it designates the specific country or region of the number, enabling proper routing of calls internationally.

This requirement ensures that every E.164 number is unique across the globe, facilitating international communication. For example, a number like +1 555 0123 represents the country code for the United States followed by a specific local number. Without the country code, it would be challenging for telecommunication systems to establish connections correctly.

In addition, while it is true that E.164 numbers can only include numeric characters and can have up to 20 digits in total (including the country code), these points alone do not capture the essential aspect that the presence of a country code is a defining feature of E.164 standardization. Formatting with hyphens is also not a requirement of the E.164 format; such formatting is often for readability purposes but does not affect the structure of the phone number in its standard form.