I feel like I've read 7 or 8 different articles on the Messages beta, but I'm not seeing my question's answer.
So, is it possible with Messages for OS X, to receive SMS texts sent to my phone number?
No. Messages beta works like it does on the iPad and iPod Touch. You can only message other Apple iOS 5 (or Messages) users.
To avoid confusion, we might be speaking about two things here:
is it possible with Messages for OS X, to receive SMS texts sent to my phone number?
Yeah it's like bassplayer7 said - it is because iMessage goes through Apple's own network and the normal sms go through the carrier's network.
Since the iPad and iPod Touch do not allow for the carrier part, they are capable of receiving iMessages and so it is the same for the Mac.
Since SMS is a byproduct of the mobile telephone technology GSM it isn't possible. SMS needs a phone number as the receiver, and that phone must eventually be connected to the network to receive it. The Mac has no GSM connection.
There could be services that receive and forward SMS to you, but I'm not aware of any, and even then, you wouldn't receive these in iMessage.