1. A method for generating speech from text, comprising the steps of: storing a set of decision tree context-dependent phoneme-based units of a target speaker, wherein a central phoneme-based unit is selected from a group consisting of a phoneme and a diphone, wherein each context-dependent phoneme-based unit is arranged based on context of at least one immediately preceding and succeeding phoneme-based unit, and wherein one context-dependent phoneme-based unit is chosen to represent each leaf node in the decision trees; obtaining a string of phonetic symbols representative of a text to be converted to speech; selecting stored decision-tree based context-dependent phoneme-based units from the set of decision tree based context-dependent phoneme-based units based on the contexts of the phonetic symbols; and synthesizing the selected context-based phoneme-based units to generate speech corresponding to the text.