For four days (from 5am GMT Thurs 24th to 5am GMT Mon 28th) Localphone, a 4 year old company based in Sheffield, UK, is offering free calls to the U.S., no strings attached. Truphone offered a similar promo in 2009. A Localphone rep told me, "Customers can call for as long as they want and to as many people as they want and we won't charge them a penny. This offer is open to all Localphone customers, new and old. Customers can call from their mobile, landline or computer using our different calling options. Customers can also download our free iPhone App and make calls on the move. Alternatively they can make free VoIP calls from our Internet Phone or their own VoIP compatible device."

You can find out more information about the promotion here.
Localphone, founded in 2007, is based in Sheffield in the UK and we offer a number of cheap international calling and SMS services