While a customer is on hold, it would be ideal to offer admin capabilities to control the music and/or messaging that is played. Few ideas related to this...

1) Customers want the ability to control the music in general

2) Customers want the ability to insert marketing messaging in the on hold experience

3) Customers should have the ability to control what marketing messages are heard based on their customer profile (ie - what products they own, what products they've shown interest etc)