How to raise free SIP-telephony?

Question

SIP

How to raise free SIP-telephony, with the ability to call mobile numbers?
Well, or how to reduce the cost of SIP-telephony, if you can't make it for free, only outgoing calls are a priority?

Answer 1

There is no free, free only within your own infrastructure.
If there was a free option, it would bankrupt cellular, IP, and conventional telephony operators.

Well, or how to reduce the cost of SIP-telephony

There are two ways:
1. look for the SIP operator with the lowest prices;
2. raise your PBX (Asterisk, etc.), use a GSM gateway (such a piece of iron, with a SIM card) and look for the most advantageous tariff plan from mobile operators (the choice strongly depends on the required number and duration of calls and on the directions of calls ).