phones4u
Ok lets say you have a prepay mobile phone from, ooh i dunno, lets say an operator called "yellow".
You can also get a prepay top up card that you can use at most point-of-sale (POS) terminals in the UK. You pay, they swipe your card, the phone is topped up, everyones happy.

Now, use all your credit up. It must be ZERO.

Lets imagine a supermarket called "Alfresco". You could gather some produce from the shelves - a few cheap items, and join a queue for the tills. As they scan each item, half way through, ask them to top up your phone - £50 will do, and hand over your prepay top up card. The scanning recommences. Your topup goes through. Take your phone out and dial a number, make sure it connects, burn up a few pence of credit.

When you are told the amount for your sale, make sure you have mysteriously forgotten your wallet, say you have enough for the scanned produce, apologise and ask them to refund the top up. The top up you havent yet paid for, but crucially - have used partially. They will do this - its called a 'reverse' in the world of POS. There will be an error on the system but it will not be processed properly by the Alfresco 'front-end' till which will happily carry on, having removed the £50 top up from the sale. The backend system will flag an error in a log file somewhere and move on. The cashier will see nothing, the till will work as it always does, its not really a till anyway.

You pay for your goods, and leave. You notice that mysteriously your phone seems to have about £49.85 worth of credit on it. Funny that.
( I have run out of coke is a little sweaty, Thu 18 Oct 2007, 15:49, 1 reply)

Very nice
I'll be putting this into practice ASAP.

Cheers
(Pavlov's Frog figures no-one really reads sigs anyway, Thu 18 Oct 2007, 18:10, closed)