Ok berrycorp, just noticed you posted whilst I was writing my last reply. I can help ya now.
Your offering voip calling solution, have a look at what voipfone(.co.uk do, they have an automated system set up to call the customer, give them a pin code to enter before they will process the transaction.
Your offering voip calling solution, have a look at what voipfone(.co.uk do, they have an automated system set up to call the customer, give them a pin code to enter before they will process the transaction.