Normally if reception presses DND with the phone still on the handset a menu comes up for night and day mode. However, lifting the handset before pressing DND means it will respond like a normal handset.
In order to set an unconditional forward (i.e. all calls) the receptionist will have to do the following:
1) Lift the receiver
2) Press DND
3) Press 1 for unconditional forward
4) Enter the group number to forward to (i.e. 624)
5) select ok
6) replace the receiver
To turn the forwarder back off:
1) Lift the receiver
2) Press DND
3) press # to cancel the forwarder
4) press ok
5) hang up the receiver
Hope this helps