plug into the earplug jack of an iPhone or iPad

plug into the earplug jack of an iPhone or iPad “When debit cards were introduced in the early ’90s, that was the beginning of the slow and gradual decline of paper checks and cash,” said Red Gillen, a senior analyst at Celent, a research and consulting firm on technology and financial services, based in Boston.

Still, cash has remained essential in certain instances, like paying back a colleague for lunch, buying fruit at a farmers’ market or buying a beer at a cash-only bar. These new mobile payment technologies could finally change that.

“The problem with cash is that it is tangible, it’s inconvenient, you have to carry around a bunch of bills and you have to continually go to the A.T.M.,” said Jack Dorsey, a Twitter co-founder who is now the co-founder and chief executive of Square, which makes a dime-size device that anyone can plug into the earplug jack of an iPhone or iPad to instantly accept credit card payments. “If we can make cards more convenient and faster, it can replace a lot of the experiences around cash.”

Light wallets are not a problem for Joe Mangrum, a sidewalk sand painter in New York, who has been using Square to take donations from passers-by and sell copies of his book. Sales have increased sharply since he started accepting credit cards on his iPhone, he said. “I’ve made the sale as opposed to twiddling my thumbs because they don’t have the cash.”

The new services could have the biggest impact on the smallest businesses, like farm stands or house cleaners, that accept only cash and checks because they do not have stores to house credit card terminals and do not want to enter into complicated, long-term relationships with credit card companies.

Rachel Ancliffe, a clothing designer in Portland, Ore., sells her dresses and blouses at sample sales and from her home, and uses Intuit GoPayment to process credit card payments.

“You can’t accept checks because then you’re just kissing your product goodbye” because of fraud and bounced checks, Ms. Ancliffe said. “I sell 10 times more because I take credit cards.”

Fraud protection offered by the credit card companies is the same as when the card is used at a cash register. Some of the new companies say security against fraud might even be improved because DVD Ripperthey provide e-mail receipts, and those from Square include photos and a map of where the transactions were made.