Scrive can send PIN by SMS codes to mobile phones in over 80 countries. For several other countries, some restrictions may apply, typically a pre-registration process to enable the service in a given country.
The conventional way to log in to a web service is with a username and password. These are both things the user knows, so it only counts as single-factor authentication. Since these can be compromised, it is more secure to require an additional authentication factor, typically something the user possesses (a physical device like a mobile phone) or a biometric identifier like a fingerprint. PIN by SMS became a widespread method of two-factor authentication because almost everyone has a mobile phone.