At Bolt (https://bolt.co https://bolt.co) we use Twilio for this, and I'm pretty sure WhatsApp does too along with other providers. With Twilio we also fall bac

At Bolt (https://bolt.co https://bolt.co) we use Twilio for this, and I'm pretty sure WhatsApp does too along with other providers. With Twilio we also fall back to delivering access tokens with a phone call when the SMS fails. (Full disclosure: I am a former Twilio employee.)