It’s an interesting solution to the spam problem: require users to have a mobile phone to sign up for an email account. This is the approach Google has taken with the recent launch of their Gmail service.
Spamming is all about volume: they have hundreds of IP addresses, thousands of email accounts to spam from, with large spammers sending out literally billions of messages. The only reason this works is that each of these resources is cheap or free, and easy to deal with in large quantities. In fact, one of the suggested solutions to spam is to charge $.01 per email sent. A normal person sends a few emails per day and wouldn’t even notice the one or two dollars per month added to their ISP bill, but spammers would (theoretically) be out of business.
In the same vein, the moment you require something like a cell phone to obtain an email account, you’ve made it difficult for spammers to obtain a large chunk of accounts, which makes it easier to disable them if it’s discovered they’re being used by spammers.
Let’s hope it works.