13 files declare their use of SmsGatewayInterface in SMS Framework 8

DefaultSmsProvider.php in src/Provider/DefaultSmsProvider.php

DeliveryReportController.php in src/DeliveryReportController.php

Incoming.php in tests/modules/sms_test_gateway/src/Plugin/SmsGateway/Incoming.php

RecipientGatewayEvent.php in src/Event/RecipientGatewayEvent.php

RecipientGatewayEventTest.php in tests/src/Unit/Event/RecipientGatewayEventTest.php

SmsFrameworkGatewayEntityTest.php in tests/src/Kernel/SmsFrameworkGatewayEntityTest.php

SmsFrameworkTestTrait.php in tests/src/Functional/SmsFrameworkTestTrait.php

SmsFrameworkUserAccountRegistrationServiceTest.php in modules/sms_user/tests/src/Kernel/SmsFrameworkUserAccountRegistrationServiceTest.php

SmsIncomingController.php in src/SmsIncomingController.php

SmsMessage.php in src/Message/SmsMessage.php

SmsMessageInterface.php in src/Message/SmsMessageInterface.php

SmsMessageProcessor.php in src/EventSubscriber/SmsMessageProcessor.php

SmsProviderInterface.php in src/Provider/SmsProviderInterface.php