Mobile-phone cash register Square open for business

(CNN) -- Square, an application that turns a smartphone into a mobile cash register, is open for business.

Created by Twitter co-founder Jack Dorsey, Square uses a free download and plastic card reader to let users accept credit card payments.

The app charges users 2.75 percent of the transaction cost plus a 15-cent fee -- a rate Dorsey said is in line with what retail stores pay for accepting cards.

"No one carries cash any more," Dorsey told CNN's "American Morning."

"Everyone carries a little plastic card and nobody carries their checkbook. So being able to accept credit cards means more money, more volume."

The app will benefit small, independent merchants as well as fundraisers, Dorsey said.

The app is available for several phones using Google's Android system -- including the Droid, Droid X, HTC Evo and Samsung Galaxy S -- and the iPhone, iPad and iPod Touch.

Perhaps not surprisingly, Dorsey announced that the buzzed-about app had gone live with a post on Twitter.

"The doors are (finally) open @Square & we're going big," Dorsey tweeted on Friday.

The app can be downloaded at Square's official website or the app stores for the different operating systems.