15. A caller adaptive telephonic voice response system capable of interacting via a telephone line with a caller by generating voice messages recognizable by said caller as audible speech spoken at a predetermined speaking rate and by detecting a response from said caller to said voice message within a variable response time interval, the system comprising: (a) means for generating over said telephone line at least one voice message recognizable by said caller as audible speech spoken at an initial predetermined speaking rate and for generating over said telephone line at least one subsequent voice message recognizable by said caller as audible speech spoken at a subsequent predetermined speaking rate, said subsequent voice message being generated by said system subsequent to said voice message; (b) means for detecting over said telephone line a response from said caller; (c) means for measuring said variable response time interval, said variable response time interval being indicative of the elapsed time between the end of a voice message most recently spoken by said system and the detection of said response from said caller to said most recently spoken voice message; and (d) means for adjusting said initial predetermined speaking rate to said subsequent predetermined speaking rate, said adjusting means being responsive to said measuring means so as to adjust said subsequent predetermined speaking rate to a rate higher than said initial predetermined speaking rate if said variable response time interval is shorter in duration than a first predetermined amount of time.
17. An apparatus according to claim 15 further comprising means for determining if a caller response is an expected response and thereby a valid response and determining if a caller response is not a valid response and therefore an erroneous response, and wherein said adjusting means is further responsive to said detecting means so as to adjust said subsequent predetermined speaking rate to a rate lower than said initial predetermined speaking rate if said caller performs an action selected from a group consisting of no response and an erroneous response.