There are many VoIP services that offer free calls to USA. Some of them are:
1) ViatalkFree:
Vitalk offers this service; this is a phone service provider service in USA, with this you can make a free call for 10 minute each time you call. This phone service is restricted to US, if you are in another country you will not be able to get this service.
Free Calls
Free Calls
2) Callingamerica
They also offer cheap calls to USA, they recently blocked some countries to make calls to USA one of them is India. It is available for many other countries.
3) Poketalk:
This free calling service also offers free calls to many major countries of the world including USA.
4) RingtoNumber:
These providers also offer free calls, but you need to register with them. They will give you a short code to make the call to the desired number.
5) icall:
These are one of the best VoIP service providers in USA. They offer free calls to US, they have however reduced the number of free calling minutes, and you can only call 3 minutes for free.
6) MediaringTalk:
This VoIP service has been offering free calls to international destinations for almost 2 years now. They offer 10 monists free call to USA, their services are very good, and the quality of sound while calling is also perfect. In order to make free calls you will have to download mediaringtalk softphone.
7) Tuitalk:
This service also offers free calls to USA and many other countries. You can call 5 minutes for free to USA, it also depends on the country you are calling from.
Voixio:
They offer 30 Minutes FREE daily allowance.
Free calls are also made to many countries including USA.
9) Gizmo5 Backdoor Dialing:
This service also offers free calls to certain phone numbers in USA, not all phone numbers are available but you can try your luck.
10) Ringplus:
This is also an access number based calling service. They offer free calls to USA and many other countries.
So this was a list of free calling service to USA. I hope you would have liked it and will certainly try.