According to this official document from TRAI, Free SMS in any form will be limited to 100 per day and no more. Now if you are wondering why, blame those numbers which were sending you unnecessary SMS of free job, free PAN service and so on.
Updated : The Limit is Set to 200 now
Yes you got it right, the telemarketers who misused the SMS pack from the operators.
The Authority is also aware that unsolicited commercial communications can be/are being sent by unregistered 52 telemarketers. Such messages can be sent by any person and they are essentially in the category of P2P communications. However, in order to curb such messages, the Authority has decided that no Access Providers shall provide any SMS packages in any form (through voucher, student pack, seasonal pack etc) permitting sending of more than 100 SMS per day per SIM except on blackout days or days specially notified by TRAI.
Any such package already in use shall be withdrawn w.e.f 31.12.2010. Provisions have also been made to disconnect the telecom resources after giving a notice if it is found that telemarketing activities are being done from the unregistered telemarketer.
This is documented in Page 51 , 52 point 18. If you remember TRAI did roll out tough regulation for Telemarketers in December.
Overall this is a good step to restrict to an extent but it will be still tough for a customer as there is no place where they can call and register a complain. A telemarketer will have more then 3-4 SIM on an average and with SMS packs costing them peanuts, TRAI will have to figure out more ways to curb them.
Another sgement which will be affected on this are students who are the major buyers of SMS packs and this will directly impact the operators who are making lot of money for charging high on SMS ( call charges are lower these days ).