Please note that I have changed "telephony" to "telephone". The Free Dictionary gives the definition of telephony as:
1. The transmission of sound between distant stations, especially by radio or telephone.
2. The technology and manufacture of telephone equipment.
I assume you're not having a demo of how sound is transmitted between stations, and I thought it was unlikely that you are having a demo of the technology and manufacture of phones. Am I right in thinking that you have had a new phone (net?) system installed and an engineer is coming to demonstrate how it works? If not, apologies and telephony may be correct.
Student or Learner