6 files declare their use of SmsMessageResult in SMS Framework 2.1.x

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

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

SmsFrameworkMessageTestTrait.php in tests/src/Functional/SmsFrameworkMessageTestTrait.php

SmsFrameworkProcessorTest.php in tests/src/Kernel/SmsFrameworkProcessorTest.php

SmsFrameworkResultUnitTest.php in tests/src/Unit/Message/SmsFrameworkResultUnitTest.php

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