OK, in the last few days, I've received - missed actually - on average two calls a day from a particular number. Trying to call the number back results in a "the number you are calling is not connected" RVA. Tried it from three different phones just to be sure.
Telemarketers / charity? Don't think so, they are supposed to have at least some announcement indicating what organisation you have called in to, even if it doesn't result in you connecting to a real person.
Something a little more sinister then? What's your thoughts on this?