Ok, so here's the next bit.   The most important bit of the solution is the box that reads the caller ID information from the incoming phone line and squirt that data down a serial connection.

I use a box from a company called Crucible technology.    I'm using A BT (British Telecom) phone line, here in the UK.   I can only vouch for this working in this setup.

Here is a link to the box...

http://www.crucible-technologies.co.uk/mall/productpage.cfm?store=TeleProducts&productid=MP&did=43864

As for the rest of the hardware,  its the following -

Compaq Ipaq 3600
Compaq Ipaq Extension Cradle - gives the Ipaq a PCMCIA card slot.
Old 3Com 802.11b PC card - which had pocket PC drivers.
9 Pin Serial cable, to Ipaq.

OK, in the next (hopefully exciting) episode, I'll go through the software elements that glue all this together.

Happy Easter All...