Software & Plugins for Speex 

http://speex.org/projects.html a list of projects with Speex support

BitWise IM 

BitWise Chat is a cross-platform instant messenger that integrates voice chat and uses Speex for the audio compression.

Features 

http://www.bitwiseim.com/features.php

BitWise IM is…

Packages 

BitWise Personal

is for personal/home use and is free. Personal may not be used for any business or organization.

BitWise Plus

is also for personal/home use, but offers additional encryption and security features for a small, one-time fee.

BitWise Professional

is business-class instant messaging, providing administration, user rights, technical support, and more.

Linphone 

Linphone is a web phone.

Features 

Works as simply as a cellular phone. Two buttons, and one more to chat. Linphones includes a large variety of codecs (G711-ulaw, G711-alaw, LPC10-15, GSM, SPEEX and iLBC ). Thanks to the Speex codec it is able to provide high quality talks even with slow internet connections, like 28k modems. Understands the SIP protocol. SIP is a standardised protocol from the IETF (http://www.ietf.org), that is the organisation that made most of the protocols used in the internet. This guaranties compatibility with most SIP - compatible web phones. You just require a soundcard to use linphone. Other technical functionnalities include DTMF (dial tones) support though RFC2833 and ENUM support (to use SIP numbers instead of SIP addresses). Linphone is free software, released under the General Public Licence. Linphone is documented: there is a complete user manual readable from the application that explains you all you need to know. Linphone includes a sip test server called "sipomatic" that automatically answers to calls by playing a pre-recorded message.

Compatibility 

Linphone is mostly sip compliant. It works successfully with these implementations:

Linphone may work also with other sip phones, but this has not been tested yet.

Linphone uses the SIP protocol to establish calls, for that reason it cannot work with H323 phones, because SIP and H323 are different and opposite protocols. H323 phones are Netmeeting (for windows), Gnome-meeting (Unix), OpenPhone…