When set to true the state editor will display a textbox UI control for entering the SMS message.
The SMS textbox will support all the functionalities supported in the base Send SMS state, like: the session variable token
replacement, truncate message longer than 160 characters and send it as another message, etc.
When set to true, the state should provide implementation for the processMessage(SmappStateProcessingContext) method to handle
activation from the reply message of this SMS.