The problem this solves
Sometimes an external service does not send SMS to a business number. Instead of guessing, check whether voice verification or another suitable option is available.
Working cleanly
Try SMS, check whether a voice option is available and document which method works with each service. Each service may behave differently.
What to check
Verify that the number is entered correctly, the call reaches the destination and the test is documented.
Next step
If a working method is found, define it as part of the business's regular workflow.