Calling toll-free numbers in US

goodValue

A search found that Viber does not charge to call 1-800 numbers in the States, but that call quality is usually poor if it is not a Viber to Viber call.

Would whatsApp have a similar facility, or if not, are there any other apps to do this?

movedto03

Use one of the various 01, 02 or 03 dial-through numbers. The call will use your inclusive minutes. 

jbrassy

You could use Rebtel which includes unlimited free calls to US numbers.