Why almost no website chooses to send out verification code via voice call?

[JaskHill]

I set up FreePhoneLine in my OBI200.

When I sign up for an account in most web sites, I found they all choose to send an SMS verification code to the phone number ( which they demand during the sign-up process ).

Few, if any at all, sites offer to send such code via a voice call to the phone number.

Does someone know why?

Is it much cheaper to send code via SMS text than through voice call, that's why most websites choose the SMS text way?

I searched the Internet. But I cannot find any articles on this topic. Is it an industry secret than no one is allowed to disclose?

Some people may claim that now everyone owns a cell phone. So this should not be an issue. But I am not naive. I want to know the real or hidden reason behind it.

Thank you.

[ubergoober]

It's less work to code the transmission of SMS messages than a phone call that is going to have to say something.  The transaction takes far less resources in terms of time, effort and cost.

I'm not surprised you found no articles on the topic because it's mostly self evident.