Indicate are D-Bus interfaces of the daemons valid
If there's some issue with the daemons (for example, not launched at all), messages similar to this could be found at the GUI client app logs:
DeclarativeUssdUtils::DeclarativeUssdUtils(QObject*) Could not initiate UssdUtils interface
DeclarativeCallUtils::DeclarativeCallUtils(QObject*) Could not initiate CallUtils interface
QString DeclarativeCallUtils::formatNumber(const QString&) CallUtils is not initiated
CallHistoryModel::CallHistoryModel(QObject*) Could not initiate CallHistoryDatabase interface
DeclarativeDialerUtils::DeclarativeDialerUtils(QObject*) Could not initiate DialerUtils interface
It's probably a good idea to be able to indicate the status via the UI too (not just as logs of the declarative plugin).