1. Earthcaller(Only US/Canada)
They allow FREE PC to phone calls anywhere in US. You can make calls only from a PC.
2. Gizmo combination with Ringbranch (Only US/Canada)
Check out this blog entry to find out how. You can make calls from Gizmo softphone from your PC, or you can use your VOIP phone/ATA device for calling. Right now limited to 1000 minuts of call per month.
Allows free calling between two US numbers. Enter the two numbers in their website, and they will call and connect both of you. If you reside in another country, you can still work it out if you have a incoming US number mapped to you SIP device(eg sipnumber service)
4. JustVoip (Many countries)
Supported countries :Argentina,Australia, Austria, Belgium, Brazil,Bulgaria,Canada,Chile,Colombia,Cyprus,Czech Republic,Denmark,Estonia,France,Germany,Greece,Hong Kong (+mobile),
Hungary,Ireland,Italy,Japan,Latvia,Luxembourg,Malaysia,Mexico [guadalajara],Mexico [mexico City],Mexico [monterrey],Monaco,Netherlands,New Zealand,Norway,Panama,Peru,Poland,
Portugal,Puerto Rico (+mobile),Romania,Russian Federation,Singapore,Slovak Republic,Slovenia,South Korea,Spain,Sweden,Switzerland,Taiwan,Thailand,United Kingdom,United States (+mobile),Venezuela
You can make free call from this site. You need a phone number in one of the above countries to call to these locations. If you reside in another country, you can still work it out if you have a incoming US number mapped to you SIP device(eg sipnumber service)
Calls are limited to 5 minutes. They allow you to make international calls to many international destinations from any phone. You will be given local dial in number and a PIN to call your destination. You do not require any hardware/soft phone. In India, they currently allow calls only to Hyderabad landlines. They are going to introduce calls to other parts on India May 1st
By this facilty, you will get a conference dial-in in many countries. People in India can call their own local number to connect to the conference.