There was a Bugtraq local exploit alert for speechd versions up to 0.54. Download version 0.55 (not yet tested).

speechd - Implements /dev/speech (any text written to /dev/speech will be spoken aloud).
Last updated Thu Sep 13 14:52:44 EDT 2001

The speechio.faq has info on increasing the volume of speech, and dealing with RedHat's broken /etc/hosts file, which will give you errors similar to "rejected from localhost.localdomain not in access list".