1. A method for providing text-to-speech (TTS) functionality to a telematics unit of a telematics-equipped vehicle, the method comprising: receiving text content to be played back by an audio system of the telematics-equipped vehicle; determining, by a processor, a TTS rendering process to be used for the text content from a plurality of TTS rendering processes, wherein the plurality of TTS rendering processes include local TTS rendering using a local TTS engine at the telematics-equipped vehicle and remote TTS rendering using a remote TTS engine at a communications center; and causing, by the processor, the text content to be rendered as an audio signal for playback by the telematics-equipped vehicle using the determined TTS rendering process.