Spoke to soon! I wonder if anyone can help:
Set this up this afternoon on one 'phone. Works perfectly. To keys, programmed to "Single Line" and each display a different caller ID when I dial out.
Then tried to do it on another 'phone. Set up the key as a Single Line, gave it another Directory Number (as it wouldn't let me use one of the same ones as on the other 'phone). Set up that Directory Number in Associated Directory Numbers using CPN substitution... but nothing. When using that key to call out on the second phone, it displays the DDI set for that extension in Associated Directory Numbers, not the one for the button.
EVERYTHING is the same as the first phone - same handset type (5330), same Class of Service...
I must be missing something but can't think why it won't work. Can anyone steer me in the right direction please?