(CNN) -- Square, the mobile app and hardware that turns a smartphone into a cash register, is now letting users send and receive money as easily as sending an e-mail.
Square Cash can be used between friends, say as a way of paying back a buddy for picking up the tab last night, or for small businesses that have been using its plastic card reader to accept credit card payments.
"Square has always believed in creating solutions for individuals and businesses that work with the tools they already have in their pocket," Brian Grassadonia, head of the Cash project, said in a post on Square's website. "Square Cash makes it convenient to send money to anyone -- without making them jump through hoops to retrieve it.
"Now it's easier than ever to split a bill, send a birthday gift, or settle up with a friend, no matter where you are."
Sending money via Square Cash will be free, according to the company's post.
Created by Twitter co-founder Jack Dorsey, the current Square model charges 2.75% of the transaction cost plus a 15-cent fee -- a price in line with what larger retail stores pay in order to accept cards.
Users don't need to sign up to use Square Cash. Someone can simply send an e-mail to the recipient, with firstname.lastname@example.org cc'ed and the amount of the payment as the message's subject line.
That user will then receive an e-mail prompting them to link a credit card to their account. The recipient enters a debit card number once, and will have that account associated with their e-mail afterward.
The service launched Tuesday and is currently only available in the United States.
Founded in 2009, Square offers services that are available in the United States, Canada and Japan.
Since then, it has added products like an iPad-holding countertop register and an app that lets users do a mobile check-in at participating businesses and pay even if they don't have a credit card with them.