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(Pocket-lint) - Paying with your phone is the next big thing, but while many are talking about it, actually doing it is  still something that's fairly difficult to achieve at the moment.

There are schemes and systems in place, like the Starbuck gift app or the Barclays Pingit stickers, that go some way to allowing us to envisage what the future holds, but the banks on the whole are still in the process of seeing where the dust settles.

Visa, however, has already started a trial with 800 carefully selected people from the world of banking, key industry influencers, Olympic athletes and Pocket-lint to see how paying with your phone in the real world will actually work.

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That's right, for the past couple of weeks we've been using a Samsung Galaxy S III to pay for things up to £20 around London at a range of different shops to see whether paying with your phone will become the defacto payment method in the future.

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Visa anticipates that by 2020, 50 per cent of transactions over the Visa network will be made by a mobile device. That's a lot, so you can see why it is keen to get it right from the beginning.

With that in mind the payWave software we used in the run up to the London 2012 games - where Visa is a key sponsor - is just for the trial. Unless you are one of those 800 you won't be able to buy it, download it, or ever be able to ever use it yourself - sorry.

The idea is for Visa to show banks how easy the system is, how easy the software is to use, and how easy it would be for a bank like Lloyds TSB, who Visa is working with for the trial, to implement the following technology into an app of its own.

After going through a lengthy set-up process before we got the SGS3 (setting up a bank account and completing a series of security checks) we picked up the phone, loaded £50 on to the account and went in search of somewhere to spend it.

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The NFC for this trial, or payWave or tap to pay as some like to refer to it, is in the SIM card rather than on the phone's own NFC chip. That means it can be used when the phone is off, or out of battery and, Visa say, allows the security to be tighter as it is tied to the phone number rather than the device.

It makes a lot of sense and would allow you theoretically to retrofit NFC into several devices rather than worrying about whether or not the phone comes with NFC. It also means that when you sell your phone or upgrade it you won't have to worry about transferring security details to the new handset.

The app itself is incredibly easy to use. Although basic it gives you a running total of your current balance, the ability to top up the account and authorise payments.

To pay, all you have to do it hover the smartphone over the payment terminal, authorised the payment, type in a pin and that's it. Done.

If you think that sounds like a faff, it's not.

In most cases, especially the places most commonly featuring the specific NFC readers, you'll probably have your phone in your hand checking your email or Twitter updates while you are in the queue - we certainly did, and not once did we experience any problems paying with the new method.

At the moment the system is restricted so you can't pay for anything costing more than £20 and Visa tells us there are around 140,000 contactless payment systems in the UK.

These include all McDonald's, the Post Office, Subway, Nandos, Eat, Timpson, Caffe Nero, Pret A Manger, Paul, Greggs, Little Chef, David Lloyd, Crussh, PayPoint, West Cornwall Pasty, the Slug and Lettuce pub chain, and numerous other shops and restaurants - although once you start looking it is surprising the number of outlets that don't offer contactless payment.

You've no doubt spotted a trend in that list, and for the moment the main places to spend with your phone are sandwich bars and fast-food outlets. Remember the system only works with payments under £20 at the moment.

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That £20 limit is as much about security as it is about making people feel confident about loading up their phone with cash.

Visa has told us that those on the trial who go to the Olympic Village will be able to spend more, because it has a greater control over the payment infrastructure at the Games. If it goes well, expect to be able to make bigger payments when NFC payment apps start appearing.

So the big question, will it replace your credit card altogether?

There is no reason to see why not when it comes to smaller payments. The only real problem we experienced with the trial is finding shops not listed above that feature the contactless payment machines. Starbucks, for example, doesn't have them, nor will your high street butcher.

But we can see that if you have the phone in your hand and need to make a payment quickly, there is no reason why you couldn't use this as an alternative to save getting out your wallet or your purse when you reach the cashier. 

Writing by Stuart Miles. Editing by Adrian Willings.