Hi,
Excuse my lack of knowledge - I'm not a phone guy. This should be a pretty easy one.

I have a Panasonic KX-T7630 handset. I want to set up 2 DSS keys (the 24 hotkey things on the right of the phone) so that one diverts to voicemail (ext 399) when busy or no answer, and another DSS key diverts all calls to a mobile number.

Any help much appreciated :-)

You have to program the entire string for each forwarding condition. Example, for cf/bsyna to voicemail you would program the button for dialing string "*7105399#"
All calls to the mobile would be "*71029(mobile number)#"

I'm assuming the Australian codes are the same as the US codes. But it can be figured out by looking in the manual.