When you register your phone with a mobile service provider, they store any personal information that you provide, so consider the advantages and disadvantages when deciding whether or not to register your phone. If you purchase a mobile phone (and a SIM card, if necessary) without having to provide identification, and if you buy prepaid "minutes" for the phone using cash, then there is no immediate link between the phone and your actual identity. Wherever possible, keep your private identity and personal activities separate from your work and other activities.