Gmail Sign up For FREE (Home)
Official Google Blog: "Sign up for Gmail"
Long back when Google services were available to people only on invite.
But when Google open its services to all the people around the web, it started to give invitation with sms confirmation, After getting verification code on your mobile, you can easily sign up and enjoy Google service.
But now a days, you can easily sign up, no need of extra pain taking business, no invitation required as Google itself taking care of spammed and using Internet security measure which include tracking IP address.
so, we all today enjoying the Gmail services.