How to organize softphone on android?

Question

linux

Good evening everyone!
There is one idea that is not new, the technical implementation of which I can’t comprehend in any way ...
So, let's imagine that there is a server accessible from all over the world via IP-shnik. There is an application on android / ios that "can communicate" with this server using a specific protocol (for example, SIP). Each user of the application is assigned a number (a certain user ID). In the functionality of the application - FIRST - dialing this ID-number and voice connection of two subscribers who have the application. AND SECOND - making voice calls to external landline and mobile numbers.
My questions are as follows:
1. Is such a "scheme" of a software phone realizable?
2. What specialists with what knowledge can implement the project (well, except for mobile developers)

Answer 1

how to call from the phone ....
Put Asterisk, fasten the webmord to it, and hook your androids with the same zoiper ....

Answer 2

Everything was invented before you - the same Viber, Skype, etc.
There are ready-made sips on the phone and there are a lot of them. But if you need your own, with preference and heroes, then you need specialists in Java, Swift (optional here) and C # (if Windows).
If with little blood, then put any chip on the bodies, start the aster and set up the companies. PROFIT

Answer 3

1. Server - any IP PBX
2. Programs - softphones for the SIP protocol, there are a lot of them ready, google. I would recommend using the paid Bria
3. Contract(s) with a telecom operator for external calls.
You should not create a bicycle, take ready-made solutions.

Answer 4

Why are developers here? There are already all sorts of SIP softphones, so at least one Asterisk specialist is enough.
And, if you are going to make money on this, then do not forget to get a license for the provision of communication services, install SORM and certify your communication center.