How do you compete with Google's new Wallet mobile payment system? Well, a $100 million cash infusion certainly couldn't hurt. AT&T, T-Mobile and Verizon have plans to invest just that amount in Isis, sources told Businessweek. That sum is likely to grow, since taking on Google is no small feat, especially considering Wallet is already off the ground, with nationwide retail partners and support for MasterCard PayPass. Though Isis first made its debut last year, Google Wallet, which was announced in May, has clearly taken the lead. Isis is little more than a top-level website at this point, though with three of the nation's largest carriers providing support, it could have a chance to catch up -- especially if the carriers elect not to partner with Google, leaving Sprint as the sole wireless provider. We're glad to see some potential healthy competition for Wallet, especially considering that it was looking like Google was poised to create a monopoly. We expect much more to come on the Isis front, but in the meantime, hold on to those wallets -- cell phone payments may be in your future, but for now, paper and plastic are where it's at.