15. A text-to-speech system for converting text input to speech output comprising: a text disambiguation engine configured to evaluate lexemes in accordance with a set of disambiguation rules that define usage senses for the lexemes, each usage sense having a conditional statement and a significance indicator, wherein the conditional statement defines a set of conditions applicable for selecting the usage sense, wherein the significance indicator defines an effect of the associated conditional statement evaluating as TRUE, wherein the different text-to-speech results are produced by the text-to-speech system for an evaluated lexeme depending upon which of the associated usage senses are determined to be applicable by the text disambiguation engine for a particular usage instance, wherein the conditional statement includes a context range specification, wherein the set of disambiguation rules includes a first conditional statement for determining a sense of usage of a lexeme as an acronym and a second conditional statement for determining a sense of usage of the lexeme as a word, wherein the first conditional statement and/or the second conditional statement distinguishes between the sense of usage of the lexeme as an acronym and the sense of usage of the lexeme as a word at least in part by requiring a specified word within a specified context range of words of the lexeme, and to replace the lexeme with a defined full text equivalent in response to selecting a usage sense corresponding to the lexeme used as an acronym.
15. A text-to-speech system for converting text input to speech output comprising: a text disambiguation engine configured to evaluate lexemes in accordance with a set of disambiguation rules that define usage senses for the lexemes, each usage sense having a conditional statement and a significance indicator, wherein the conditional statement defines a set of conditions applicable for selecting the usage sense, wherein the significance indicator defines an effect of the associated conditional statement evaluating as TRUE, wherein the different text-to-speech results are produced by the text-to-speech system for an evaluated lexeme depending upon which of the associated usage senses are determined to be applicable by the text disambiguation engine for a particular usage instance, wherein the conditional statement includes a context range specification, wherein the set of disambiguation rules includes a first conditional statement for determining a sense of usage of a lexeme as an acronym and a second conditional statement for determining a sense of usage of the lexeme as a word, wherein the first conditional statement and/or the second conditional statement distinguishes between the sense of usage of the lexeme as an acronym and the sense of usage of the lexeme as a word at least in part by requiring a specified word within a specified context range of words of the lexeme, and to replace the lexeme with a defined full text equivalent in response to selecting a usage sense corresponding to the lexeme used as an acronym. 17. The text-to-speech system of claim 15 , further comprising: a text normalizer; and a phonetizer, wherein both the text normalizer and the phonetizer use the text disambiguation engine to resolve ambiguities.