17. A method for performing a telephone directory assistance function, comprising: for each of a plurality of calls, each call being made by a respective caller from a respective terminal having a respective telephone number: receiving a signal from an originating switch serving the respective terminal, the signal designating the telephone number of the respective terminal; prompting the caller to speak a name associated with a desired directory listing; determining a telephone number desired by the caller based on a speech signal received from the caller subsequent to the step of prompting the caller; releasing the desired telephone number to the caller; and creating a call record comprising the released telephone number and the telephone number of the respective terminal; processing according to a parameter modification algorithm a plurality of the call records to modify parameters of a speech recognition algorithm, said processing comprising calculating model parameters for a plurality of a-priori probability models, each a-priori probability model representing an estimated probability of a respective name in a name vocabulary being spoken during a directory assistance call as a function of the telephone number of the terminal from which the directory assistance call is placed; and employing the speech recognition algorithm to recognize names spoken by callers in directory assistance calls received subsequent to modification of the parameters of the speech recognition algorithm.
18. A method as defined in claim 17, wherein each a-priori probability model represents an estimated probability of a respective name in the name vocabulary being spoken during a directory assistance call as a function of an NPA-NXX portion of the telephone number of the terminal from which the directory assistance call is placed.