General Bytes offers the Twilio API to send SMS codes to you & your customers. The charges per SMS vary across regions.
NOTE: The major phone carriers around the globe impose limits upon the frequency of SMS transmission. They do this to prevent SMS spam & to provide a consistent service. The carriers use equipment that has limitations; there’s no getting around this. When these limits are exceeded, the carrier will “filter” out the excess SMS traffic, and those messages will simply be discarded: lost. You’ll commonly see these filtering events occur in batches.
GENERAL BYTES no longer offers Twilio (or Nexmo) via the GB API (paid service).
You must signup for (and deploy in your CAS settings) your own Twilio (or Nexmo) account.