Ios, how can I verify that the entered phone number is actually the user's phone number?

Question

I saw a couple of different applications (Snapchat, whatsapp, etc.) to ask users to enter their phone number. Then a text message is sent to the user with a code to verify that the number is actually their number. Then they can see which of the user's address book contacts has an application.

I understand how it all works, except how they send text messages to the user. Do they work with their own SMS gateway like Kannel using an SMS gateway provider like twilio, or am I completely missing another option?

It seems that with the help of a gateway provider even a 1 cent message will be added very quickly, especially when you are really trying to protect the application from several users who intentionally put the wrong phone number.

Answer 1

Most applications use sms gateway services, yes sms is expensive, there is another way to check the user number with a missed trick. http://dial2verify.com/