HLR is a database that stores information about all mobile network subscribers. It contains information necessary to manage the subscriber's connection to the network and provide him with communication services. HLR stores data on mobile phone numbers, SIM card identifiers, subscriber activity status. You can check any mobile number, find out the operator, subscriber status and other information with an HLR request only for the purpose of testing and checking the service. The accuracy of the information is not guaranteed, since the subscriber data is provided by a third-party mobile operator.
HLR - the query shows if the phone number exists and if it is currently active
SMS mailing
service
SS7 network
Operator
If a client has a large enough base of mobile numbers, then after a certain period of time, some numbers become obsolete, and someone changes their operator, including their number.
HLR queries are used to maintain an up-to-date list of numbers. This service helps to timely separate active numbers from inactive ones.
In other words, HLR queries help your client to manage their budget and distribute it wisely.