Isis, which was formed through a partnership involving AT&T, Verizon Wireless, and T-Mobile USA, is attempting to enter the mobile payments business at a busy time. Google has already launched Google Wallet, although it remains limited to one smartphone on Sprint Nextel, and is only compatible with merchants with newer payment terminals. Visa, meanwhile, is attempting to create its own digital wallet. American Express, which has expressed a preference to partner, on Monday said it would invest $100 million in start-ups devoted to digital payments.