In many countries people carry more than one phone/SIM card. Mostly for separation of concerns, i.e business and pleasure. Also for tariffs across providers. I

In many countries people carry more than one phone/SIM card. Mostly for separation of concerns, i.e business and pleasure. Also for tariffs across providers. It isn't unusual to have one carrier better for data and another for voice/sms. Another significant factor is contacts. If your contacts are on one network and you are on another, there is enough motivation to get a second device as intra-network is cheaper than cross-network