A telephony-based messaging system application is built for use by a particular customer. The application is stored on a computer readable medium and includes a set of modules, where each module comprises call flows, code and a Customization List. The Customization List includes one or more tables each having a list of names and a modifiable list of corresponding DTMF signal identifiers. With this architecture, the particular customer is permitted to change the mapping between caller-entered DTMF signals and the corresponding actions taken by the messaging system by modifying the list of DTMF signal identifiers, i.e., without modifying the call flows or code.