If the HTTP status code of the response is 200, among other fields, the response body will contain a confidence level.

Confidence Description
Verified Number format validated and number verified.
Absent Number format validated and number verified via network lookup but not currently available (e.g. phone off, out of range).
Teleservice not provisioned Number is assigned to a SIM card which is not allowed to make or receive telephone calls. Typically a “data only SIM".
Unverified Invalid number format supplied.
Unknown Valid number format but not verified with network lookup.
No coverage Unable to detect the live status for the telephone network.
Dead Number has been confirmed to be dead by the network and will not receive calls or text messages.