Thanks for the further responses.
An update: I checked the flag setting for my phone and noticed 'Propagate Original Caller ID on Transfer' was set to No, which I have now changed to Yes. I tested again, but was still seeing the switchboard number appear on my mobile so will contact our line provider and see what they can do. We are in the UK.
Regarding the other settings, under Users > Me > Dynamic Extension Express, I have the following set
Step1, Step timer = 30 seconds, Dest1 = Desk, Dest2 = Mobile
Step2, Step timer = N/A, Dest1 = Voicemail, Dest2 = [blank]
Under Associated Destinations, I have...
Type = Desk, Dest = 752, Active = Yes, WMI/Pullback = Yes
Type = Mobile, Dest = 07... , Active = Yes, WMI/Pullback = No
Type = Voice Mail, Dest = 2500, Active = Yes, WMI/Pullback = No
What does WMI/Pullback do?
Enable voice Detection didn't work no matter what I set for Human-Answer-Supervision. Despite answering the call on my mobile phone and talking down the phone it still did not connect the call. I still needed to hit the # key to get the call connected.
The behaviour of the DEE answer features is not consistent with that TE suggested would happen. For example, when I set Human-Answer-Supervision to Off, my desk phone stops ring when my mobile starts ringing. The two only ring simultaneously if this option is set to either Full Prompt or Tone. I tested this yesterday and again this morning and can confirm this behaviour.
Is there a flag, or other option I'm missing? Or maybe this is a bug?
Thanks again, really appreciated.