Is there any way to use multiple hadsets with the xd 5500?

I have a 3 handset HD 5500 system and would like to know if there is any way to use more than one handset at the same time like a normal extension phone. As the system is configured at present all handset ring and can be answered, however, once one is in use all of the others are unusable. Is there some way to configure the phones to function as normal extension phones so that more than one person can communicate?