What technology is used by callback and number substitution services?

Question

Telephony

There is a task to build in substitution of numbers and callback in other product.
It is necessary that the service technology has a good API
, give out phones, take money, give a connection in response.
This should definitely be a service, the numbers can be as follows: 1000 phones, thousands of minutes a day.
Give me a direction, please? links to sites?

Answer 1

Everyone makes their own service/server.
We can cooperate. Email in profile.