1. A method of generating a custom text-to-speech voice, comprising: selecting a voice for generating a custom text-to-speech voice associated with a domain; collecting text data associated with the domain from a pre-existing text data source; using the collected text data, generating an in-domain inventory of synthesis speech units by selecting speech units appropriate to the domain via a search of a pre-existing inventory of synthesis speech units; and generating a text-to-speech custom voice for the domain utilizing the generated in-domain inventory of synthesis speech units.