if the receiving person has no credit nor internet access then none would work since at least one is required.But the other person doesnt have skype, also no internet access
There was an app which lets you call people free from internet for up to 60 minutes per month and the person your calling recieve it as a regular call, but I forgot app name
Yeah you can do that.
But, you can get Skype, pay some kind of subscription and use Skype as a common phone and call phone numbers.
(Edit: Saw that last one on Skype´s ads xD Not confirmed if it works yet or not )