Bulk SMS sender addresses in India should reserve the first two characters to identify the provider and region, as per TRAI regulations. Hence, the first character is the provider and the second is the region from which the message is sent. Below is a reference for you to find out where the message originated. The characters after the first two identify the name the sender has registered with this provider.

e.g. LMCiti means the message is from Citi and is sent through BPL Mumbai. TDIRCTC means IRCTC sent the message through Tata Tele Delhi.

Provider Code
Airtel A
BSNL B
Datacom Solutions C
Aircel D
Reliance Telecom E
HFCL Infotel H
Idea Cellular I
BPL Mobile/Loop Telecom L
MTNL M
Spice Telecom P
Reliance Communications R
S tel S
Tata Teleservices T
Unitech Group U
Vodafone Group V
Swan Telecom W
Shyam Telecom Y
Region Code
Andhra Pradesh A
Bihar B
Delhi D
UP-East E
Gujarat G
Haryana H
Himachal Pradesh I
Jammu & Kashmir J
Kolkata K
Kerala L
Mumbai M
North East N
Orissa O
Punjab P
Rajasthan R
Assam S
Tamil Nadu T
West Bengal V
UP-West W
Karnataka X
Madhya Pradesh Y
Maharashtra Z
Access provider Website details
Aircel http://www.aircel.com
Bharti Airtel http://www.airtel.in
BSNL http://www.bsnl.co.in
HFCL http://www.hfclconnect.com
IDEA http://www.ideacellular.com
Loop Mobile http://www.bplmobile.com
MTNL Delhi http://www.mtnldelhi.in
MTNL Mumbai http://mumbai.mtnl.net.in
Reliance Communication http://www.rcom.co.in
Reliance Telecom http://www.reliancemobile.com
Shyam http://www.hellorainbow.com
Spice Punjab http://spiceindia.com
Spice Karnatka http://spicetele.com
TATA http://tataindicom.com
Unitech http://www.uninor.in
Videocon http://www.videocon.com
Vodafone http://www.vodafone.in

Update: Starting March 01, 2011 only transactional SMS messages are allowed to be sent with a name identifying the sender (i.e. like LM-Citi). All others sending promotional messages will have a numeric ID identifying the telemarketer.