The law mandates the functionality. How to enable and test this functionality is the responsibility of the carrier. Whether the compliance is achieved by testin

The law mandates the functionality. How to enable and test this functionality is the responsibility of the carrier. Whether the compliance is achieved by testing third-party apps or via an in-house bypass implementation is immaterial. On the other hand, assigning liability for non-compliance is tricky and for Google the jury is still out (pan intended).