Question : What are typical charges paid on a recurring basis to a carrier/gateway for using a premise-based VOIP system?

If you have your own premise based VOIP system and you are using a PRI line to connect your phone system to the internet, how do you get charged for phone calls that traverse or terminate on the domestic POTS network and for that matter how are international calls accounted for?  

In loose terms what are the basic monthly/quarterly/semi-annually or annual fees that I am looking at for this type of system?  

Answer : What are typical charges paid on a recurring basis to a carrier/gateway for using a premise-based VOIP system?

At some point you will connect to a POTS phone service provider.  They will bill you for your calls both internationally and domestically.  The PRI you are using has to connect to some service provider.  The charges associated with that may include the phone traffic.  If that's the case you'll have to contact them to break out the charges for you if they are not itemized on the bill.