Although I can't find an official press release, it appears that a lack of appetite by service providers means that we won't be hearing mobile phones in tunnels on the London Underground, at least anytime soon.
This article gives some of the reasons. The words of a journalist that refers in March 2009 to the London terrorist attacks of 'A couple of years ago', do though need to be taken with a pinch of salt.
Personally I am pleased because (i) it reduces the likelihood of the person next to me bellowing into their mobile telephone and (ii) I can't get it out of my head that allowing mobile telephone signals in tunnels would give terrorists the technical ability to do things that they cannot do at present.
Anyhow, no testing on the Waterloo & City Line and and continued peace and quiet for the rest of us. Yeah right!