A prefix code is simply a code that you dial before the number you are calling. This diverts the call from your line provider to your call provider. You are then billed by your call provider for that call. Being a manual process, it is more time consuming than alternative methods and it is easy to forget to dial the prefix code.
However, if you want to use a particular provider for a particular call, using a prefix code is the ideal choice. For example, a particular provider may offer the lowest rates to a particular country that you are calling.
