Well that's the rumour that spread around forums, SE have never said that it'll only be open to invites.
They have said "We hope to see everyone participate!", that players may receive messages that the server has reached capacity (implying they're expecting a lot more players online than they've had in the past), and that the open beta applications site is opening soon.
Yet they have mentioned that there will be open beta applications before, not to mention we got the warning from zam to use our CB keys to ensure SE sent us an OB key when it started. While we haven't been giving anything concrete, its really pointing to "Open" not "Public" so far.