What is the validation logic for phone numbers entered for SMS verification?

Hi there,

First, it's suggested to use below format when input SMS string:

+{countryCode}{phoneNumber}

(dash in the middle is also acceptable)

The validation happens at OneSpan Sign backend if you are posting from SDK, a third-party library is used to validate the number. So assuming you are pass the string as "+1-111-111-1111", this is what will happen:
(1)OneSpan Sign system will pre-format your string and convert it to "+11111111111"

(2)The third party library analyze the number and try to find the country code, in this case is "+1"

(3)According to the country code, the library will analyze the rest part. The below steps involve the internal workings of the library, so it's just my own understanding:

    (3.1)Given the country code, check the length of the rest part, which is cheap

    (3.2)Then detect if the area code is available, in this case is "111" which doesn't exist I believe. You can try to use a real region code, like "201", will make the number pass the validation

(4)The library is not able to tell if it's a junky number or not. 

Duo