mxo.walrus has confirmed that beta testing for The Matrix Online has begun for a select group of testers.  In a brief post on the official website forums dated June 1, walrus implores potential testers to be patient as beta progresses.

I understand everyone's exitement about beta testing beginning today. However, posting thread after thread saying "Geez I hope I get an email" isn't going to change what's already been stated: 1) The first wave of testers is small. 2) Beta testers can't talk about getting in on the boards. 3) No one promised to post when waves of testers would be allowed in. I said I'd check into it, nothing more. If you want to chat about your beta hopes and fears, put it in the Beta Buzz sticky-thread on the General boards. Other threads talking about beta are going to be locked, as they're just spamming up the boards. Again: Beta does begin today with a small number of testers. More will be added as needed. Please do not fill up the boards with threads about waiting for emails--that's what the Beta Buzz thread is for. We're excited about the beginning of testing, too. Let's just try and keep it orderly. Thanks, mxo.walrus

Good news for all those eager to step into the Matrix.  Beta signups are still being accepted at the official Matrix Online website.