web based sms system

[brabus]

what do i need to develop a web based sms application using php?

[pyro]

Not sure what you are asking -- that's a pretty broad question. Basically, you are going to need PHP and some sort of database. mySQL is very commonly used with PHP.

[Bootsman123]

You'll need someone to provide you with a system to 'send' the sms. The most common way is e-mail to sms. You can make an e-mail system where the (small) 'e-mails' are send to a server which handles them and delivers them to the specified phone number.