The plot thickens.

The instructions I've been given worked beautifully - thanks again. And on entering 830, the phone displays 192.168.1.8 - the address I expected to see. Default gateway is correct, subnet mask is correct.
So somewhere along the line, it's just decided to not 'talk' to the network, despite showing a connection light on the MP40- and the network switch. No change in responses overnight - still 'Destination Host Unreachable'.

831 gives me an address of 192.168.1.11, which I *can* ping - this isn't resolving a name. I'll go through the manual and find out what that refers to.

For reference - 192.168.1.9 responds and name resolution suggests voicemail; 192.168.1.10 appears to be cti.

I can change the IP address but I think a reboot is required for that to take effect. The Officeserv 7000 Series Call Server Programming book suggests a 'System Restart' option in programming which is self-explanatory... Our 7400 offers a 'System Reset' which is a little more troubling! (Probably the same thing in this scenario - can anyone confirm?)