The founder of Twitter has launched a payment system that could replace credit card scanners with mobile phones.

Jack Dorsey's idea is that anyone with a mobile and the right software should be able to accept a card payment. His new project, Square, is a dongle that plugs into a phone's audio input socket and can scan cards.

Mr Dorsey and his co-creators claim it will bring "immediacy, transparency, and approachability to the world of payments." They say paying by card is "still difficult, requiring long applications, expensive hardware, and an overly complex experience."

Photo identification confirms the user is the genuine card holder. Receipts can be sent instantly to a mobile phone or email address. The Square Web site says the product can scan cards using "any device with an audio input jack."

Mr Dorsey launched the new venture in typical style — with a 99-character tweet.

It should be available to all in early 2010.