23. Apparatus as in claim 20 wherein said each phone machine further includes: first means for generating an end-time distribution for each phone based on (a) the labels entering the phone machine for said each phone and (b) a start-time distribution of said each phone; and second means for evaluating the probability that a particular phone produced an input string of labels based on the generated end-time distribution of the particular phone.
23. Apparatus as in claim 20 wherein said each phone machine further includes: first means for generating an end-time distribution for each phone based on (a) the labels entering the phone machine for said each phone and (b) a start-time distribution of said each phone; and second means for evaluating the probability that a particular phone produced an input string of labels based on the generated end-time distribution of the particular phone. 24. Apparatus as in claim 23 including means for determining each of at least some of the start-time distributions from the end-time distribution of the most recent previous phone.