The AblePhone, a voice activated/adaptive phone. Limitations are price and conversations are not private. Dynamic living offers a Voice Activated Phone System which consists of a voice-activated speaker phone and a voice-activated phone dialer for $599; it also shares the same problem as AblePhone of no private conversations.

Asterisk is a free open source PBX and VoIP system. There’s also Tribox (formerly known as Asterisk @ Home), which is an installation package consisting of Asterisk plus other components to have a fully functional system on a PC or on-the-go. Note: Windows users need to install a Virtual Machine and a QEMU processor emulator. Here’s a great tutorial from VoipNet.

For voice recognition, there are a few open source solutions that are mostly Linux/Unix-based machines. Carnegie Mellon University developed SPHINX. Here is a very comprehensive list of other freeware and commerical Speech Recognition software.