Is it possible for the receptionist to put the current call on hold in order to answer a second incoming call?

This is not possible when using a Polycom desk phone. If all operators are on a call and a new call comes into the Main Line, it will either be answered by the auto attendant or go to voicemail depending on your call routing settings. However, this is possible when using the Dialpad app on a smartphone, tablet, desktop, or laptop computer - and it is very easy to do.