He declined to disclose many details about mobile payments at Starbucks, including how many customers use the service or what the average purchase is by smartphone.

While he wouldn't disclose future plans for the system, he did say the retailer has considered allowing smartphone users to form a separate line to pay. Today, all customers line up together to order and pay.

Davidson said that paying by mobile is faster than by other methods, and demonstrated how fast the free Android app is to use. Users will touch a button on the screen of the phone to pay, then scan a bar code that is presented on the phone display and then click once more to finish when they will see the total left on the Starbucks Card on the phone display.

With the assistance of MFoundry, Starbucks was able to build a completely different app for Android that works with Android 2.1 devices and above across various hardware manufacturers, Davidson said. The Android app is not a duplicate of the app on the iPhone he said, although it functions in a similar way.

"On Android, we have to make sure it worked efficiently with the home button and back button, optimizing what we had," he said.