Some users of Betamax services suspect the company of selling their phone numbers and e-mail addresses.
I am a current customer of two of these services and have not noticed any SPAM or telemarketing which I would suspect to be related to that fact. Nor have the explanations of those making these accusations convinced me.
I don't know whether Betamax does any telemarketing themselves; if they do it in countries where it is legal I don't see the problem with it (neither, of course, do I see any problem with attempts and strategies to thwart telemarketers — that's called freedom).
But automated telemarketing does not rely on collecting phone numbers the way e-mail spam relies on collected e-mail addresses; telemarketers generally just call all numbers in a given prefix sequentially. So unless you get a marketing call by a live person who knows your name, chances are that nobody gave out your phone number but that it simply was your turn. The same applies to SMS spam: it just gets sent to all numbers sequentially.