This is the region lock, so the smartphone is not imported into territories where it is not intended. The smartphone must therefore be activated with a European SIM card before it can be used, for example, with an American, Chinese or Australian SIM card. Activation is usually use/telephony for 5-10min. After that the smartphone can be used with any SIM card in any region. There is no influence on the use, if you ever use it with other SIMs.