Square, the brainchild of former Twitter staffer Jack Dorsey, sells a piece of plastic that fits in to the headphone jack of a phone and acts as a card swipe for processing payments on the handset.

Initially scheduled for release earlier this year, the full launch was pushed back after hardware shortages and underwriting issues led to roll out delays.

The company now claims that it is processing millions of dollars in transactions every week.

Its primary market consists of small independent traders who are wooed by the promise of cheaper transaction processing and set up costs than those found via traditional merchant terminals. Square ships the card reading device for free and charges 2.57% plus 15 cents for each transaction.

The company is also more relaxed about credit ratings, incorporating influence scores on social networks such as Yelp and Twitter into the merchant approval process.

Square is currently hiring more staff for its New York offices and is expected to apply for more capital from VCs in the near future to fuel its expansion.