Phone Verification Service?

Question

Telephony

Today I went through verification through confirmation of the phone number. Everything was simple, the number calls and you need to enter the last 6 numbers of the phone number that called. I have an advertising service where I also need confirmation through a phone number, but I use calls with the pronunciation of the code, the call sometimes costs up to 7 rubles, and there are thousands of customers, it’s expensive. I suppose that that service is many times cheaper, because there is just a ringing ... Maybe someone knows such services?

Answer 1

this smsc.ru service was perfect