What Hurdie said is spot on. Except that a lot of folks like me
What geo-market are you targeting Jivko? As Peter Johnston points out - people don't want to call. http://uk.businessinsider.com/conquer-your-fear-of-the-phone-2015-5?r=US&IR=T
I don't think you have a viable product here. You ARE going to need to use something like Twilo if you want to go forwards because the telephone numbers you want to put out there and do the connections for, are allocated by the LECs (Local Equipment Carriers). And you have to buy them in blocks and pre-pay for them
the Twilio's and Google Voices and Skypes of the world do this for you... for a fee.
But I think you seriously need to vet this idea some more. I don't think it has a meaningful market