A few years back Dialpad launched a free PC-to-Phone service inbound to anywhere in the US. This offering attracted more than 14 Million users. Today Dialpad still does millions of minutes per month and they have long since killed the free calling to the US model.
Terracall among others are now offering free inbound calling to the USA in hopes of attracting paying customers. The tactic has worked in the past, there is no reason it will not work again.
There will be more offers like this, stay tuned.