Though Apple’s digital assistant is only available on the iPhone 4S, you can get a taste of Siri on your Mac using OS X’ integrated Speech functionality. “Samantha” (a.k.a. Siri, clip below the fold) is the default voice on new Macs running Lion. However, if you manually installed Apple’s latest operating system on your Mac, you will need to download and install her to hear that melodious voice — here’s how to get it done.
On your Mac running OS X 10.7 or later, open System Preferences, navigate to Speech and tap the Text to Speech tab. Put a check in the “Speak selected text when…” box.
Next, in the System Voice drop down menu, select Customize.
In the resulting pop up, put a check in the box next to Samantha (and any other voice you’d like to add), tap OK and give Download a tap, too — voices are relatively large files, so this could take a minute or three.
Once your download is complete and the files installed, head back to System Preferences > Speech > Text to Speech and select Samantha from the System Voice drop down — give the Play button a tap for sample.
Now in any Apple (or compatible third-party) app, highlight a paragraph of text, press Option + Escape and Samantha (a.k.a. Siri) will read it to you. This is a system wide keyboard shortcut and something you should explore — it’s a great proofing tool.
OS X’ “Samantha” voice is the same as Siri on the iPhone.