Vonage has an app that permits making phone calls from an iOS or Android device.
See
I downloaded it and installed it on my Android phonr. I was able to make phone calls, apparently for free, to non-Vonage numbers. I'm a Vonage customer but I did nothing to associate my account with the Vonage app.
The menus indicate that you can call Vonage subscribers for free. But, I called a Verizon landline. The caller ID was for my mobile number. I verified that this works with the data networking turned off on my device.
They say:
Get FREE calls to any landl* Free calling service is for personal, non-commercial calling to the United States, Canada and Puerto Rico, and does not include calls to certain geographic locations, premium and special services numbers, satellite telephony services and other call forwarding services. Not to exceed 3000 minutes per month.
Are they really giving away minutes or am I missing something?
Clearly, options like this make it hard to figure out the per minute cost of telephone service.
Chuck