Posted to another forum about this and it seems as though I've got the answer. I don't have a smartphone, but it looks as though Facebook has found my phone number in the lists of contacts of other people I know who have chosen to share those contacts with Facebook (or possibly Facebook has taken the details without permission). Whichever way round it is, I regard it as an infringement of privacy. I do not give out my contact details to people for them to be shared with giant corporations.