PayPal, Google Wallet, and Apple Pay will vie against a known quantity as Amazon offers its payment system to other merchants.
Sprint wireless users will be the first Amazon Prime members able to take part in the program though their wireless carriers on a monthly basis.
On Friday the state will order remote sellers to collect and remit sales tax. Catalogers want to mount a legal challenge.
Walmart Pay marks the retailer's exit from the Merchant Customer Exchange consortium that includes Target, Best Buy, and CVS.