Ask Slashdot: Linux and Telephony

This one is a doosy. I've received various submissions from people who were looking for information on how to make their Linux box into an answering machine. I've also received submissions asking about Voice Synthesis and Speech-To-Text. I have to admit I haven't found much information on either while browsing on the net, so I'm turning the question over to you folks. However I wonder if there isn't a issue hidden here? Can Linux be used as an Interractive Voice Response(IVR) platform? If not, why not? First off, let's NOT forget the actual questions:

Metiu and Sri both want to know if a Linux box with a voice modem can be used as an answering machine.

Gextyr is looking for information on Voice Synthesis packages that are available for Linux.

This Clan AC Member wants to know if there are any applications or APIs for Linux that deal with Speech-To-Text or Text-To-Speech.

Lastly, there have been quite a few submissions asking whether or not Linux can be used as a demand fax server. Can it?

If Linux can be used for all of the things above, what's stopping it from performing as an IVR system? IVR systems are simply systems designed to use a telephone as the computer interface (using both touch tones and voice). IVR systems are used everywhere, from your voice mail, to ordering systems, and corporations are adopting more and more IVR systems for various tasks.

I've seen IVR implemented on DOS systems but most of these have moved to NT. What's preventing Linux from operating in this market? Are there existing IVR projects in progress, or is this another area where Linux falls behind?