I want to develop a voip billing system in php and mysql. Do you gays able to help me by giving me some tutorial links.Or some technical suggestion as how to start and how can I do it final.Thanks all in advance for reading my query and trying to help me.

Tutorials on what? What do(n't) you know?

I think it is more important for you to have the billing process defined before you start to develop your application. Also, with regard to storing data, you'll need to figure out what type of data you need to store and how the data is related. Then, the last phase is just applying a front end-application.

check out voicephp on google. tringme on google.
They are viop techs in php.
I guess they might help.

In connection with VoIP developments in PHP [I can recommend you this guide]<URL SNIPPED>. It offers many example projects with free source code.