Calling America lets you make free USA voip calls.  Calling America as the name implies is mainly for making voip calls to anywhere in the USA.

Ad Supported free voip calling
Voip Calls with Calling America are free because you  need to listen to a short ad before each call.  This essentially pays for the call you are making.

Calling America voip features
A few of the features we like with Calling America is 1) No download needed, 100% browser supported. 2) 15 minutes total free talk time. 3) Ability to call 1800 numbers,

To get started visit http://callingamerica.com/