Yep! It's sh4speech. Get it here:
http://www.subsim.com/radioroom/showthread.php?t=119430
As downloaded, it won't work with RFB without some tweaking, but stock and TMO versions are OK. I can send you the tweaked files for RFB by PM if you want. It's a stand-alone program that runs in the background when SH4 is loaded.