Jack Dorsey, who co-founded Twitter, has just announced his newest venture. It's a mobile payment service called Square that is currently in a limited beta stage but plans to 'go live' for everyone in early 2010.
Square allows its customers to accept credit card payments on their mobile phones or laptops by using a small magnetic strip reader that connects via the headphone socket, avoiding the need for dedicated credit card processing equipment and the associated charges. It currently works on the iPhone and iPod touch.