Text message (SMS) verification for signups

Question

I have seen a disturbing trend where websites are starting to require verification sent to cellphones by text message (SMS). Gmail and Facebook are two of them. What I want to know are the following:

1. Is it a good idea to start requiring cellphones instead of emails now?
2. How do I do it on my own website?

Edit

Here are some of my new questions on the topic in response to the answers:

1. I see that most of you are saying that SMS registrations is ok. But what about the people who don't have cell phones? And why is it accepted to give out your cell phone information freely?
2. Do those big providers really pay per message to a gateway service? Is it not possible to set up a server with the correct SMS software, or at least buy a subscription directly instead of having a middleman?

Answer 1

Most SMS Gateway services have some kind of API. An HTTP interface seems to be the norm.

Just make sure you sign up for a service that allows receiving of messages because not all do. It's more work for them since they have to send some kind of data back to you.

Some services offer send receipts too which lets you see if the receiver got the SMS.

Some examples follows.

• Esendex API docs
• TxtLocal

In regard to question number one, I think Commander Keen's advice is sound.