If you wish to send just a summary invoice using our Porta Billing Private Label VoIP Softswitch, you need to request Support to create a single and not a multi page invoice template.  You can also upload your own logo in the invoice template. Invoices by default are sent out the night of the 1st of every month. Under your customer class option, you will need disable (or uncheck) the option to send call history statistics to every customer. Porta Billing will then send out just a summary invoice to your customers under your own brand name. Porta Billing can then charge the customer’s card on file automatically.

Alternatively, you could enable the periodic payment option and just bill your customer’s card either using the balance driven or date driven option. Balance driven option allows you to bill your customer based on a certain balance amount. Example if balance drops less than $50, recharge account another $30. Date driven option allows you to bill client say $35 every month on say the 25th and so on.

Porta Billing can also bill client subscription progressively (meaning daily prorated amount) or complete amount at the end of the billing cycle.

Billing options are controlled in the customer classes link.

This Invoice Templates Billing pdf explains in detail how to setup your invoices with your logo (please contact support to get the latest pdf) and taxes for your clients under your own brand name.
You can upload your own logo to appear in the invoices that you send out. You can also have Porta Billing compute taxes etc using standard or third party plugins.
You can have Porta Billing send out the bills at preset dates.
Clients can then send in their payment or pay online  using your own merchant account.
Porta Billing has excellent billing features for managing your voip customers. Porta Billing not only manages all your Radius services but also have an extensive billing software built right into your voip switch.So Porta Billing has very rich subscription based billing features.

Please visit http://docs.globalink.us/CloudSoftware/VoIPSwitch/PortaBilling/ for more details.