You must do two things. The first is that you must verify an additional e-mail address to be associated with your Apple ID. The following is an Apple turorial which will explain how you do that. http://support.apple.com/kb/HE68
The second thing is to add this address as an alternate to your macbook Facetime App. I think you can do this on your MB by opening the Facetime App, then click on Facetime preferences from the drop down menu which will appear after clicking on Facetime in the upper left hand corner of your browser page. You should now be able to add another e mail adr to Facetime. I don't run Mountain Lion so I don't know exactly how this will work for you.
Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
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To send messages to non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8
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You can check the status of the FaceTime/iMessage servers at this link.