We do the same as MicrodigitUK but I have hit a small issue that Microsoft don't seem to want to help with. We populate ours with some AD attributes that we sync from AD -
%%Firstname%% %%Lastname%%
%%Title%%
%%Department%%
Direct Line:
xxxxxxxxxxx Ext: %%phonenumber%%
Mobile: %%mobilenumber%%
Fax: xxxxxxxxxxx
The problem I have is that as an admin I have set a recovery number in O365 for my account and in AD I have no mobile number. Microsoft are populating the field in my signature with my personal mobile number (I have no work mobile, and don't want one!).
I have put a dummy number in AD but that doesn't work, so I am stuck with my number in my signature unless I really complicate things and have an exception set just for me. I tried hiding the number in O365 profile too, but that failed. Really annoying.
If anyone knows a way to stop this easily, I would love to know.