- Everyone has a phone number
- Everyone has a US phone number
- Everyone has a mobile phone number
- Everyone has only 1 phone number
- Everyone can receive SMS
- Everyone can receive SMS at all times
- Everyone has a fixed residential address
- Everyone can check their snail mail
- Everyone sits at home all day and never travels
(Edited to add) This list is good, but is perhaps overly generous - it leaves off the most common irritant: programmers who believe that all phone numbers are exactly 10 digits, American-style, even if there is a country code dropdown.
https://github.com/google/libphonenumber/blob/master/FALSEHO...
- Everyone has a usable phone number, a residential address that conforms to your validation criteria and can receive SMS - when transiting through an international airport and attempting to use the Wi-Fi.
- Nobody's phone number has a space in it
Sometimes the phone-number input field won't let me type the last digit, unless I first remove the space. Sometimes it declares the number invalid if it doesn't have a space. The form never has hints as to what they consider a valid phone-number to look like.