I want to setup a directory service for mobile phone. i.e a service like company names and address location.?

this will be access through mobile phones such as GSM, when a user send a pre-defined keyword sms to a shot code, the name of the company searched will be returned as sms. What would I need to run this kind of service?

An SMS gateway and a computer.

On the computer you’d need a database and software to read the SMS, search the database and send the return SMS.