Cash registers and customer service desks may soon be a thing of the past.

Retailers and restaurants are increasingly turning to mobile technology to give customers instant service. They're using all kinds of devices that are changing the way we shop and eat.

Apple stores led the way, casting aside the cash register years ago in favor of on-the-spot payments with Apple devices. Now others in Fresno are following. Servers at Carrows restaurants use Android tablets instead of order pads and Casa de Tamales uses a smartphone to take credit card payments at farmers markets.

Some retailers created their own devices, such as the mini computers that Macy's clerks at the Fashion Fair store use to see whether a shoes size is available without having to run to the back room.

Although there still are some consumer trust issues to work out, more businesses are turning to the devices because they speed up service and are convenient and portable.

Shoppers likely will see more devices at large retailers, said Mike Gatti, a senior vice president at the National Retail Federation, the Washington, D.C.-based retail trade group.

"It's a competitive thing," he said. "You really want to stay leading edge and provide this great experience for customers."

'Do you have that in a 6?'

The Fashion Fair Macy's is one laboratory for this new frontier. Macy's calls its device the Enterprise Locator System; the company is using it at 100 of its 850 stores.

Gone are the days of a clerk walking a shoe to the back room to determine whether the customer's size is in stock. Now, the clerk whips out a device about the size of a remote control. After a quick scan of a bar code on the shoe, the clerk types in the customer's size and, voilà, the machine immediately tells whether the store has the shoe in stock.

But it's not done there. The device sends a message to a worker in the back room, even telling the worker which of two doors is closest to the customer to deliver the shoes.

The minutes per sale that are saved is valuable time on busy weekends when the shoe department is besieged with customers, store manager Rick Earnest said. In the time workers once spent searching for the shoe, clerks can help up to four other people, or introduce the first customer to other options, Earnest said.

"The amount of comments about not having enough help in the shoe department was probably reduced by 80-90%," he said.

Mom-and-pop restaurants and retailers have turned to mobile devices, too.

The Casa de Tamales restaurant started taking payment via smartphone at its booth at The Vineyard Farmers Market in February.

The restaurant uses Square, an application that can be used with smartphones and iPads. It was created by the co-founder of Twitter.

Now general manager Jose Aguilar plugs a tiny square of white plastic into the headphone jack on his phone. He types in a customer's total bill and swipes the credit or debit card through the slot in the square. The customer signs on the phone's screen using a finger. A receipt is sent as a text to the customer's phone or via email.

Square charges 2.75% of every transaction -- higher than standard store-based credit card readers -- but does not have any upfront or monthly fees. The device is free.

The restaurant's owners estimate that not having a credit or debit option cost Casa de Tamales hundreds of dollars in sales. They use the device at the twice-weekly Vineyard market and the Clovis Farmers Market on Friday nights.