Saad,
First you will need sometime of radius server to handle the billing and accounting so that when people pay for 1 hour of time, they only get 1 hour of time. Then you will need to sign with another carrier/provider to take your outgoing traffic and send it where it needs to go.
I am not sure I understand the part about the 6th phone, it sounds like instead of a phone, you need to have a phone line from the local phone company for people to call in on.
Mike