Configurations providing a reusable stream model for a user interface over SMS for interacting with one or more interactive systems in a parallel manner are described. An SMS server can implement the reusable stream model in which an available number from a sequence of numbers (e.g., a block of numbers) is assigned to a user session upon receiving an SMS message to initiate the user session from a communication device. The user session corresponds with a message stream for the interactive system. In one aspect, the SMS server places each number from the sequence of numbers in a respective status to indicate whether the number is currently assigned to a user session. When a subsequent SMS message is received that requests to initiate an additional user session for another interactive system, the SMS can assign the next available number from the sequence to the additional user session.