GMail Open To Anyone With a Mobile Phone

One account per phone number rule seeks to keep out spammers and bots.

BetaNews | Google Opens Gmail Service to Public
When Google unveiled its instant messaging client yesterday, there was only one problem: Google Talk requires a Gmail account, which has been invitation-only since its beta debut in 2004. This changed on Thursday, however, as Google opened Gmail to anyone in the United States with a mobile phone.