Though this thread hasn't been a sticky in quite some time, it did serve it's purpose during a time that invites were the only means of getting a gmail account. Eventually, invites became numerous enough that the sticky was cut loose.
For awhile, new members could sign up, provided they had a mobile phone to receive a text message.
The invites, and the need for a mobile phones are no longer needed.
Gmail has now become public. Anyone can sign up at the Gmail site. The members still hold invites they can send, but it's hard to figure why they would.
Anyway..... Anyone can now sign up without an invite.