You can activate SMS vouchers, GPRS packs, 3G data RCVs offered by BSNL through SMS. Cost of the voucher will be deducted from your main account balance. 

Here is the list of some of the codes though it is not complete, if you know any other codes please let me know. For activating STV by SMS see special tariff vouchers page

GPRS Activation/Deactivation:

Send GPRSPRE to 53773 for activation
Send GPRSD to 53773 for deactivation

GPRS/3G/MMS Settings:

Send <make> <model> to 58355
Ex: Nokia 6300 to 58355

Friends and Family Numbers Addition:

Send FFE <number1> <number2> .... to 53733
Ex: FFE 9491xxxxxx 9492xxxxxx ....  to 53733

Friends and Family Numbers Modification:

Send FFM <old number> <new number> to 53733
Ex: FFM 9491xxxxxx 9492xxxxxx to 53733

National Do Not Call Registry:

Send START DND to 1909 to activate
Send STOP DND to 1909 to deactivate

Mobile Signal Complaint:

Send SIGNAL to 9400054141

Deactivate Unwanted VAS Service:

Send STOP to 155223 to deactivate

ISD Calling for Prepaid:

Send ACT ISD to 53733 to activate
Send DEACT ISD to 53733 to deactivate 

Mobile TV:

Send MYTV to 55447(not toll free) for 2G customers
Send MY3GTV to 55447(not toll free) for 3G customers

BSNL Caller Tunes:

Send BT ACT to 56700(Rs.2/SMS) for activation
Send BT DACT to 56700(Rs.2/SMS) for Deactivation
Send <song code> to 56700(Rs.2/SMS) for song selection with code
Send <song name> to 56799(toll free) for song search


Send BILL to 53733 for getting the last bill amount
Send AMT to 53733 for getting the usage amount
send email Email-id to 53733 for getting mobile bill by email.