Can I disable voice calls for Verify?
Verify flows are optimized for different markets, but we do tend to attempt sending an SMS and then fail over to a voice call.
For fixed [landline] numbers we will always use a TTS (Text-to-Speech) call.
For mobile numbers we might start with SMS then attempt a TTS call if the SMS does not result in a successful PIN submission.
We are not able to customize the flow used for the Verify to use only SMS without any voice calls.
Based on our experience with conversions for many customers, we would consistently recommend verification via SMS with failover through TTS, because in the end this strongly increases the likelihood of a successful verification. Voice communication networks will always be more reliable than messaging, and so if the first SMS is not delivered, a subsequent attempt to deliver the code via a TTS call is more likely to be successful than attempting a second SMS.
With respect to user experience - explicitly informing users that they should expect an automated call has worked well for our customers, and avoids the code recipient being surprised by the phone call.