21 files declare their use of SmsMessageInterface in SMS Framework 8

AccountRegistration.php in modules/sms_user/src/AccountRegistration.php

AccountRegistrationInterface.php in modules/sms_user/src/AccountRegistrationInterface.php

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

DefaultSmsProvider.php in src/Provider/DefaultSmsProvider.php

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

LogGateway.php in src/Plugin/SmsGateway/LogGateway.php

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

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

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

PhoneNumberProvider.php in src/Provider/PhoneNumberProvider.php

PhoneNumberProviderInterface.php in src/Provider/PhoneNumberProviderInterface.php

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

sms.tokens.inc in ./sms.tokens.inc

Token callbacks for the sms module.

SmsFrameworkPhoneNumberTest.php in tests/src/Functional/SmsFrameworkPhoneNumberTest.php

SmsFrameworkProviderTest.php in tests/src/Kernel/SmsFrameworkProviderTest.php

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

SmsGatewayPluginInterface.php in src/Plugin/SmsGatewayPluginInterface.php

SmsMessage.php in src/Entity/SmsMessage.php

SmsMessageInterface.php in src/Entity/SmsMessageInterface.php

SmsMessageProcessor.php in src/EventSubscriber/SmsMessageProcessor.php

SmsProviderInterface.php in src/Provider/SmsProviderInterface.php