Short codes are mobile numbers that are significantly shorter than regular mobile numbers (usually 10 digits) which are used for SMS, MMS and Interactive Voice Services. The idea behind short codes is to make them easy to remember. For example: the short code 5-6161 in India, Messages sent to a short code can be toll free or – in most cases – more expensive than a regular SMS.
Short codes are used for buying content, interacting with a help menu, voting on TV programmes, listening to mobile radio, and a host of other services. Telecom operators, VAS service providers and TV channels use Short Codes for generating revenue.

Alphanumeric Short Codes

As per TRAI guidelines, SMS's are sent according to the following alphanumeric format: XY-SenderName, where X refers to the service provider and Y refers to the service area.
If you receive an SMS from AD-ZSMSDL, that means that the SMS has been sent by ZSMS, originating on Airtel's network, from the Delhi service area. The codes mandated by TRAI are as follows:

Service Provider Codes (X): A: Bharti Airtel and Bharti Hexacom B: BSNL C: Datacom D: Aircel and Dishnet Wireless E: Reliance Telecom H: HFCL I: Idea Cellular, Aditya Birla Telecom L: Loop Telecom and BPL M: MTNL P: Spice Communications R: Reliance Communications S: S. Tel Ltd T: Tata Teleservices, Tata Teleservices Maharashtra U: Unitech Group of Companies (Telenor) V: Vodafone Group of Companies W: Swan Telecom Y: Shyam Telecom Service Area Codes (Y) A: Andhra Pradesh B: Bihar D: Delhi E: UP (East) G: Gujarat H: Haryana I: Himachal Pradesh J: Jammu & Kashmir K: Kolkata L: Kerala M: Mumbai N: North East O: Orissa