In connection with the abolition of mobile slavery and the emergence of the possibility of changing the mobile operator (switching to another) while maintaining the number (MNP), a problem arose associated with the unknown to the subscriber which network you are going to call or send SMS. To determine which operator a subscriber belongs to, there is a mobile phone carrier lookup service https://bsg.world/ru/products/mnp-lookup/ Checking a mobile operator by number helps to reduce the cost of sending messages to non-working mobile numbers or to the wrong operator.