Email Caller ID on Call Forward

I have a couple of Trixbox installs where, out of hours, a call forward is set up on a Linksys SPA-922 (using the soft keys on the phone) to go to a duty mobile phone. As the duty mobile number depends on the person on call, I people to be able to set it before they leave.
This works fine, but the number presented the mobile phone is the office number, not the call that’s being forwarded. The same happens when I use *72 to set up the call forward in asterisk.
So if the caller hangs up without leaving a message on the duty mobile’s voicemail, there’s no way of knowing who was calling, so that they can be contacted direct.

What I’d like to do is create my own module, based on the call forward one, that sends an email (ideally an sms, but I can hopefully work round that) with the caller id and time they called, to the duty mobile.
So far I’ve downloaded the Call Forward module and essentially renamed the variables and picked a new set of feature codes. I’ve got to the stage where I can install the module through Module Admin in FreePBX. When I dial *62 (the feature code I chose for unconditional call forward) , I get taken through setting up a call forward, but when I dial the extension, it just rings, no attempt is made to dial the external number.

From what I can see the Call Forward module sets CF, CFB or CFU for an extension and these get checked when the extension is dialled. To keep my changes separate I set CFE, CFBE or CFUE. But these don’t get checked when the extension is rung. Am I missing something obvious, that will cause asterisk to check these variables when an extension is rung?