My 2004 XK8 has the Alpine sound system with in-dash cassette and remote 6 CD changer. The head unit and left steering wheel control indicate that this unit was capable of an integrated cell phone as well, but mine doesn't have this component.
I am curious about this component but can find no information about the parts or operation. Can someone point me to the details?

 

The OEM phone was a corded handset in the centre console, with the electronics module behind the back seat. There was also an ancient bluetooth version available on the later cars. Your best option though is to forget the outdated OEM phone system and get an aftermaket bluetooth system fitted instead. Lots of threads on the forum. Use the forum search feature by browsing on a desktop, rather than mobile and use the search box at the top of this forum to get X100 results:-