1. A method of controlling telephony sessions for telephony clients that are independent of a service provider, the method comprising the steps of: providing a platform server operated by the service provider; providing an interface for use by at least a first application developer associated with a first client for specifying at least a first interactive telephony (IT) application in a scripted language that includes application program interface (API) extensions associated with different IT functions; receiving input via the interface at least selecting and ordering the IT functions to specify at least the first IT application associated with a first calling number; storing the at least a first IT application in a database accessible by the platform server; receiving a call from a first customer to the first calling number; running the first IT application that is associated with the first number to elicit information from the first customer independent of the first client; and in response to input received from the first customer, linking the first customer to a specific phone extension associated with the first client.