Well, you need at least the whole of US & CA anyway. So if you have either CNNT NA ALL or Lower 49 US with AL/CA without a single tile missing it should be ok. Assuming you're using an American TTS voice, you also need one of the US dialect srd files depending on whether your unit uses the ASR1 files from 3790/2460 or the ASR2 files from 24/25/34/35xx. The former is English_American.srd and the letter is en_US.srd and the srd file is also located in the ASR folder. If you have the wrong type of srd that's also a problem.