Startup Idea : Missed Call As An Alternative to OTP

Over the time we have seen there were several protocols introduced over web for customer identity verification OR human verification. The most famous were Captcha and SMS One Time Password based verification. But these solutions do not just have loop holes but at the same time are costly too ( as the normal sms sending costs about 1-5 Cents per sms )So the overall idea is to build a Missed call based alternative to OTP and Captcha ( which would not just help in building a cleaner and trusted user-base but would be cost effective too, resulting in 85-90% cost cutting for SMBs )