I need to consider the billing types service providers use. The first question is which is better: postpaid or prepaid billing? I have found a really good interpretation of prepaid billing. According to it:
”Prepaid billing means that you have an account that you can fill up by paying for credits that can be used for phone calls. In this case when you call a number your credit decreases according to the call. You can only talk for the time your credit is valid.
When your credit went down you can fill it up in different ways, for example by purchasing a fill up card or money transfer. Once your credit is filled up, you can call others again.”
I have found the above information at the website of Ozeki VoIP SIP SDK. (voip-sip-sdk com/p_461-home-voip html)
Could you please give me more relevant information on billing?