The present system uses dynamic assignment of key codes to select options of response content in request messages prior to transmission from an application server to a communication device. Dynamic assignment of key codes to selection options can occur according to a list of key codes having a predefined order also known as a predefined key code series. A key code series could be ordered according to ergonomic considerations or other considerations such as according to an alphabetic or numeric ordering. Communication occurs between one or more server applications running on an application server and a particular communication device, such as a cell phone. Dynamic key code assignment addresses problems raised when one communication device is concurrently carrying on more than one session with one or more server applications since the communication device identifier, such as a phone number, will be the same for all sessions.