Have you heard of Square yet? It’s one of many start-ups looking at mobile transactions, but it has one advantage that, played correctly, could help it get the vital currency that any start-up needs… mind-share and users.

Square hopes to provide a low cost way for individuals and very small businesses to accept credit and debit card transactions. A small magnetic strip reader plugs into the headset socket of a smartphone (initially either those running Google’s Android OS or the iPhone), and this can be used to take payments from people through their phone. The goal of course is to give everyone access to card payment facilities and allow small transactions to be made in the real world – in roughly the same way that Paypal has opened up small payments over the internet.

And the secret sauce in all this? Square’s founder, Jack Dorsey. He’s already taken one crazy idea and turned it into a force of (internet) nature. By taking Twitter, and its idea of 140 characters per message and creating a new type of social media, Dorsey is already in the media spotlight… and he’s making the best use of that capital and spending it to promote his new company Square.

There are countless stories of start-up founders who think they can change the world – there are less about a founder who has already done so, and is attempting to do it again. And Dorsey, already plugged heavily into the Silicon Valley scene thanks to Twitter, is able to cash in and get much more press and conference keynotes than your average start-up, especially those in the financial sector.

Mind you, I still think that the best wheeze Dorsey has is that every time he demo’s the service, he manages to collect a few dollars from the person watching the demo – which is then donated to Charity Water.

You can read more about Square at www.squareup.com.