In Verify phone numbers with the Sinch Verification API , an approval callback decides whether a code goes out, based on the calling code and how often a number asks. That policy doesn't know what kind of line it's sending to. The Sinch Number Lookup API can: One call returns the line type and the carrier of a number. This post puts that call in front of the verification start. Mobile numbers get an SMS, landlines get a phone call, and numbers Lookup has no record of are blocked. For a VoIP number the code returns a challenge decision and stops, because the challenge itself, such as a CAPTCHA, belongs to your signup flow.…