I know this is off subject, but alan14 as raised a good point. The other day I was involved with a local central heating engineer, and on completing our discussion, I had a return call which I could hear him 'faintly in the distance' having a conversation with someone else. On his visit I mentioned this to him, and instantly he knew what the problem was. The 'sensitive' phone had also redialled the previous (my) number as well.
I would not have thought this possible, but apparently it is?.