Telecoms, banks, financial giants and startups -- plus Google and Apple -- are all scrambling to outflank and out-innovate each other in the mobile payments field.

By Stacy Cowley, CNNMoney tech editor

FORTUNE -- If you want to get a smackdown going, throw together five executives each angling for a lucrative piece of a $4 trillion market.

The retail payments space is one of tech's hottest battlefields. The reigning technology, magnetic stripes on debit and credit cards, is nearing the end of its 50-year run -- "it's just the U.S. and sub-Saharan Africa" left clinging on, quipped Verifone (PAY) CEO Doug Bergeron -- as NFC (near field communication) chips embedded in smartphones and other devices begin their ascent.

A new way of making payments opens the door for innovation. It also gives an army of new players the chance to try to wedge themselves into the payments stream.

Google payments chief Stephanie Tilenius wants to see phones replace payments cards.

"There's huge potential here -- it's like Amazon in 1999," Stephanie Tilenius, Google's vice president of commerce and payments, said at Fortune's Brainstorm Tech panel discussion on the mobile payments field.

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