It's simple:
Login remotely to your Linux based home computer via ssh.
Create a text file with the contents you want to say in it.
vi ilu.txt
Lisa, I love you.
:wq
Then run festival with the following arguments
festival --tts ilu.txt
If all runs well your computer speakers will say what you have written in the text file.
I get a kick of this, as I often have trouble reaching my wife via telephone. I have used this [festival], and various other methods to communicate with her when she is not logged into any messenger service or reading her email.. I once crafted a VoIP SIP packet with the caller-id "CALL YOUR HUSBAND" and sent it to her PC to be picked up by her call monitor - the actual VoIP line was down, so this prompted her to turn on her cellphone.. I was glowing when it worked! =c )
My latest tactic was to use zenity to display a dialog so I could get a response from her. example:
zenity --entry --text "What does the error say honey?"
Using the --entry option she is able to type a message and press ok, and I get the response in the ssh window as a return value.. I love that she is not using windows anymore...