Hello
I have gone through your post and understood that you need to build an app which can detect fake call and app should be subscription based . I am experience so i cam assure you that you will receive quality product .
I am 4+ years experience in making android and ios app . i would like to inform you that i have worked in all area like restaurant and hotel business,health care,e-commerce ,real estate, taxi booking etc .
if you convinced please reply as soon as possible so we can go further
looking forward to positive response
Thankyou