How to change transfer/waiting mode on my BT Freelance XD 1500?

We use BT Freelance XD 1500 phones in the office (four of them) and when transferring calls between each other the caller gets the standard 'Please hold the line, the caller knows you are waiting' message.

A client has just been telling me how outdated and irritating this 'woman' is. Does anyone know whether it is possible to change the default, silence would be better than what we have now.

Thanks