Customers can have the following types of billing:

Pre-paid, invoices for top-ups Pre-paid, full invoices Pre-paid, balance is calls only Post-paid External application None
Description This is the normal type. The customer pays for calls and transactions in advance, and their balance reflects this. They receive an invoice for each top-up. The same as "Pre-paid, invoices for top-ups", but customers receive monthly invoices rather than on each top-up. The customer pre-pays for calls, and pays for transactions each month separately from the balance. The customer pays for calls and transactions at the end of each month. Calls and transactions are exported to an external application for billing. No billing is done.
Balance is normally Positive Positive Positive Negative Zero Zero
Balance reset each month No No No Yes No No
Balance reset on invoice No No No Yes if saved No No
Calls reduce balance Yes Yes Yes Yes No No
Transactions reduce balance Yes Yes No Yes No No
Monthly fees charged Yes Yes Yes Yes No No
Credit limit Credit Credit Credit (calls only) Maximum spend per month Not used Not used
Allow top-up Yes Yes Yes No No No
Create invoice each month No Per plan Per plan Per plan No No
Create invoice on request Yes Yes Yes Yes No No
Create invoice on top-up Yes No No N/A N/A N/A
Default invoice status Pre-paid Pre-paid Due Due N/A N/A
Invoices show total due No No Yes Yes N/A N/A
Invoices show balance Yes Yes Yes No N/A N/A

In addition, there are some special purpose billing types, such as call shop telephone, which are not discussed here.