This was aired on Radio2 yesterday during the Chris Evans show, when an expert on the subject stated that many of these firms not only con people (who end up paying for two contracts with their mobile phone company), but usually go bust within a short time.
They then start up a similar business soon afterwards. Tracing them is also, apparently, very difficult.
However, some of the mobile phone companies are apparently taking a much greater level of interest in the matter (and so they should).
No doubt anyone interested in the radio interview could listen to it via the BBC website.