ENat for MSN Messenger
Have you ever met this problem when you're using MSN Messenger: Cannot voice chat or video chat with your friend, can't send a file to your friend when you or your friend are behind NATs. If you find this is very annoying, then ENat for MSN Messenger maybe a solution for you. ... Since not all of NAT devices can support MSN Messenger applcation, they can't make a voice chat if the notebook is behind a NAT without supporting MSN Messenger. ... Under this situation, MSN Messenger or Windows Messenger usually has trouble when using voice chat or video chat features except your NAT device...
http://www.easyfp.com/msn-messenger-directtalk/download/enat.exe - 1Mb - Download - Screenshot

Express Talk VoIP Softphone
Express Talk is software that works like a telephone to let you make calls from your PC. With Express Talk you can call anyone on the internet who has installed Express Talk (or any other SIP voip softphone). Calls are free. You can also call ordinary telephone numbers anywhere in the world if... ~ Works with a headset or in speakerphone mode with just a standard microphone and set of speakers. ... ~ Supports up to 4 lines on the one phone with the ability to put calls on hold. ... Features: ~ Lets you make internet phone calls free direct PC to PC, or PC to phone via a VoIP SIP gateway...
http://www.audiochannel.net/software/talk.zip - 430Kb - Download - Screenshot