Interesting point that you made “…they are very aware of the potential for mobile phones – not simply for sending SMS alerts but possibly for also mobile train display boards and the like. Something to look forward to, if they can get it working.”

Service utilising this idea is available at http://byunderground.com. It is free to use (contains some light advertisement) and is supported on all major handset manufacturers devices.
The key differentiator of the Byunderground compared to the other on-line services is its ease of use on various models of mobile devices.
With a single click on mobile device the visitor will get an overview on the current service status of each line in the underground of London network.
Line status information is presented in a table that uses colour coding that many commuters in London Underground is familiar with.
This helps to identify the line and its status quicker and in more easier way than what conventional text-based mobile sites are offering.

As it is today service offers pretty much the same (but not all!) information that is already available for mobile devices. The difference is that the information is presented in more mobile-friendly manner.
One feature that only the byunderground.com is offering is to show the duration of the service exception associated with detailed problem report. Not sure how important this is to know but it may encourage you to consider alternative routes if ‘Severe delays’ has only recently been reported on particular line.

There is also feedback form on the About page which provides the mobile interface to the editorial staff.

Moderator, sorry for turning this into cold-blooded promotional message. Just thought to share this with people with similar interests who are following your blog.

Thanks again for excellent blog entry!