One question is: who sold the data. But a more pertinent one is: who bought the data?
It is probably just a sheer coincidence that I have previously documented unexplained cold calling for T-Mobile customers from a company called LBM Direct Marketing in the UK.
This current round of cold calling is on behalf of O2. LBM appears to have subscriber details - when they finally do talk to you rather than putting the phone down, they greet you by name. [..] The caller denied that they worked for LBM, and claimed to be working for O2 [..]. Our attempts to talk to a supervisor at LBM resulted in the caller putting the phone down. In this case, they do seem to know the name of the subscriber ([..] the phone had previously been with Vodafone and then transferred to T-Mobile)This is probably not an isolated incident - expiring mobile phone contract leads are valuable and are regularly traded, and we're not just talking about T-Mobile here.. it seems to be very widespread, and T-Mobile deserve some kudos for tackling the issue.
Just in case you missed all the furore, T-Mobile have a news article about it: