In order to protect interests of consumers receiving unsolicited commercial SMSes, Telecom Regulatory Authority of India (TRAI) has mandated all mobile operators in India to prefix an identification tag before all application-to-peer (A2P) commercial bulk SMSes which would reveal the name of the service provider and location where the SMS originated along with the name of the company sending the SMS.
The alphanumeric identifier should be of the form XY-Name of the company where X stands for code allocated for the service provider while Y stands for the service area where the SMS is originating from.
For example, AT Citibank would mean that the SMS is sent through Airtel mobile network from Tamil Nadu by Citibank company.
Similarly VX stands for Vodafone -Karnataka, TA for Tata Teleservices-Andhra Pradesh, TM for Tata Teleservices-Mumbai, AM for Airtel-Mumbai, AX for Airtel-Karnataka, DT for Dishnet Wireless-Tamilnadu etc.
To answer the second part of your question, it is not possible to comprehend how did TRAI derive this as there can be no logical explaination.
For example in the first prefix, C stands for Datacom Solutions, D for Aircel, E for Reliance Telecom, P for Spice Telecom etc.
That's precisely why BPL Mobile Communications Ltd. decide to adopt a new name Loop Telecom Pvt. Ltd. as the symbol allocated to it by TRAI was L instead of B.
Similarly in the second prefix, Z stands for Maharashtra, X for Karnataka, Y for Madhya Pradesh, V for West Bengal, L for Kerala, I for Himachal Pradesh, S for Assam etc.
