Here it depends on having a pre-paid card or a monthly 'contract'. If you buy a prepaid, that is completely anonimous, but if you want a phone with a montly contract, you have to show your ID, so they could track you if the money on you bank account is to low and they don't lose money because of that.
I think buying a phone card and be registerd has 2 sides. On the one hand it indeed could be good to track spammers and such, but on the other hand you lose again a little bit of privacy

. Though... with all the extracted phone calls and intercepted text messages... what is private nowadays

. Anyway, having to register when you buy a phone number, makes you think you have less privacy, while on the other hand you've never had any, but think you have