How can I verify a phone number other than SMS?

Question

SMS

Good evening everyone!
For one application, I am developing a registration flow by phone number. I know that phones are usually confirmed by SMS code, but the customer does not like this option because of its high cost.
I would like to know if it is technically possible to implement phone number verification with a push notification? The registration flow is as follows
: 1) I fill out the first form with the introduction of a phone number;
2) I get to an intermediate screen, where I am asked to wait for the push or send it again;
3) I click on the push, thereby confirming the phone number;
4) proceed to the second stage of registration and fill in the remaining account information

Answer 1

And what are you going to confirm by pushing, the device?)
The meaning of SMS is that the phone number belongs to a person, and the push is sent to the device, that is, by pushing you only confirm that the one who tries to register from this phone does it from this phone)
Cheaper options this is a registration confirmation by call - either answer the call and they dictate the code to you, or they call you from a special number, the last four digits of which are the same code that you need to enter .
For example , here

Answer 2

Yes, there is a completely free way. You can take people at their word.