Number Portability Lookup provides you with a means to find the network of any mobile subscriber from their mobile phone number by HLR Lookup.
A lookup can be performed in realtime during call setup or SMS delivery
What is the HLR (Home Location Register)?
The HLR or "Home Location Register" is at the core of every GSM mobile network worldwide. The HLR is a central database of all customers authorised to use the network, and is used by the network in the authentication of a phone when registering with a transmitter, either on the home network, or when roaming abroad.
The SS7 Network
Operators around the world are connected by a network known as the "SS7" or "Signalling System #7" network. This network is used for exchanging information related to setting up a telephone call, number translation, prepaid billing systems, and also forms the backbone of the SMS (short message service) text messaging system.
HLR Query - How it works
By sending the appropriate message over the SS7 signalling network, it is possible to query the home location register (HLR) of any mobile subscriber using their phone number. This process is known as performing a "HLR Lookup" or "HLR Query", and is a fast, effective, and accurate way to determine which network operator currently serves a given mobile telephone number.
Benefits of Number Portability Lookup