Mr. Nemoy just said:
"This is the day. Spock speaks to Sheldon on The Big Bang Theory tonight. I had a wonderfull time. Thanks to a great company. LLAP"
https://twitter.com/#!/TheRealNimoy
Check your local listings!
http://www.cbs.com/shows/big_bang_theory/video/2214143546/the-big-bang-theory-the-transporter-malfunction