How to create an app for international calls?

How to create an app for international calls, so you can directly call to the phone number as it does TELZ, VOIPSCAN? Can you tell me the article or examples. I never understood how they work. Maybe some kind of service know. Maybe through the Api need to work. Prompt please who faced. Technology article prepared open sours app, book anything so I know where to go. Thanks in advance)
April 4th 20 at 00:54
2 answers
April 4th 20 at 00:56
Probably should start here.
With this technology a little familiar. But the question is how to call directly to phone number and not using the Internet calling - Zackary.Cremin commented on April 4th 20 at 00:59
April 4th 20 at 00:58 you Can start with Russian laws.
Then read the legislation of the other 148 countries.
With the theme of pairing of IP and terrestrial telephony, you can see on the example
Well, to start to read

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