Verizon Wireless, AT&T and T- Mobile USA take the fight to Google Wallet.
Isis was created last year as a scheme to enable subscribers of the three networks to load up NFC-enabled phones with cash, which can they use to pay for goods at retailers with a suitably compatible reader.
It was originally conceived as a proprietary network using its own payments tech to collect and share out payments, and charge fees on every transaction.
But in May it scaled back its ambitions in favour of hosting a mobile wallet as a repository for multiple partners and thus opening up their existing in-store infrastructure.
Now Bloomberg has spoken to insiders who confirmed the $100m injection, subject to how successful Isis is at attracting banks and merchants.
It already has the support of American Express, Discover, Mastercard, and Visa.
Of course, the race is on in the contactless payments area with Google Wallet, which was unveiled in May
The service will work with existing Mastercard PayPass kiosks at participating retailers in selected cities – first San Francisco and New York City, with a nationwide roll-out to follow. Signed up retailers include Macy's, Subway, American Eagle, Walgreens, Container Store and more.