Have got a project idea where i would like to build a database ( no problem)containing list of items and their description, a user can send an sms to ask about a product. Gsm modem connected to a pc receives the message.the messageis used to query the database and send the information needed to user's mobile phone immediately. The headache is building the application in the pc to use the sms to retrieve info from the database and send it back. Anyone ever built such a thing before

information on resources needed and way to go about it will be highly appreciated

apart from the SMS part (which is simply a matter of hooking up some libraries any service provider should be able to provide you with as part of a contract for their services) this is something that's probably been done by everyone who's ever written anything.

And if you substitute other communications technology, that's pretty much a certainty.

The SMS part is also far from unique.

So any search engine should be able to provide all the information you need.

I actually did some similiar work on a website not too long ago. I wanted users to be able to send information from a cellular phone to their account on my website. I used an email account, however, and used some IMAP libraries to enable a .NET script to check the email account periodically (about every 5 minutes) for new messages. The script then scanned the message for the data I was looking for, stored it in a database, and replied to the sending "email address" that the data had been received. To simplify things, you might try that approach.