7 files declare their use of SmsMessageInterface in SMS Framework 2.1.x

ActiveHours.php in modules/sms_user/src/ActiveHours.php

ActiveHoursInterface.php in modules/sms_user/src/ActiveHoursInterface.php

DefaultSmsProvider.php in src/Provider/DefaultSmsProvider.php

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

SmsFrameworkMessageEntityTest.php in tests/src/Kernel/SmsFrameworkMessageEntityTest.php

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

sms_user.module in modules/sms_user/sms_user.module

Provides integration between the SMS Framework and Drupal users.