[ebzlo]

Twilio has an API to identify the provider. https://www.twilio.com/docs/lookup/api

Still costs money, but if you're sending a lot of messages, this would substantially reduce the costs.

[rsync]

"Twilio has an API to identify the provider ..."

  curl -s -X GET "https://lookups.twilio.com/v1/PhoneNumbers/$number?Type=carrier&Type=caller-name" -u $accountsid:$authtoken | /usr/local/bin/jq '.'

[remram]

If you're sending a lot of messages through one of those, you can expect to be blocked pretty quickly unfortunately.

[colinmhayes]

Just try them all...