Xbox.com says so.
August 17, 2007 - If you've been following our coverage on Call of Duty 4, then you know that getting into the upcoming Xbox 360 exclusive multiplayer beta is a prize worth fighting for. A recent update to the official Xbox 360 Marketplace ticker indicated that the beta, or news on it, might be coming sooner rather than later. There you could find the Call of Duty 4 Multiplayer Beta listed as a new arrival for today, August 17, but the listing has since been removed.
If you're thinking that news came out of left field and that you missed the boat on signing up, you're not alone. A call to Activision placed by IGN confirmed that the beta is not available to the public just yet and nothing has been announced. According to an Activision spokesperson, "No official availability date for the Call of Duty 4: Modern Warfare Multiplayer Beta has been announced, but stay tuned to Charlieoscardelta.com for upcoming details"
Perhaps this showed up as a snafu in the submission process? What it means to us is that you should keep your finger on the trigger; the beta is on the way