Google has expanded the selection of credit and debit cards that can be used in its mobile wallet app, a move that could make the service more attractive to consumers.

The release of a cloud-based version of Google Wallet comes amid sluggish consumer adoption of the service, which is only available on six phones from Sprint and Virgin Mobile.

The app lacks support from AT&T, Verizon Wireless and T-Mobile USA, who are working together on their own mobile payments service.

The updated version of Google Wallet supports credit and debit cards from Visa, MasterCard, American Express, and Discover. Before, only two cards could be used to make payments through Google Wallet, the company's own prepaid card and CitiBank's prepaid card.

The app now stores payment information on "highly secure" Google services, instead of on the phone itself. The changes allow users to load their existing cards into Google Wallet, instead of signing up for Google or CitiBank's prepaid cards or waiting for their bank to support the app.

For banks that do want to get on board with Google Wallet, the new cloud-based approach "speeds up the integration process for banks so they can add their cards to the Wallet app in just a few weeks," Google Wallet product management chief Robin Dua said in a post on the company's blog.

Google also made the app more secure by allowing users to remotely disable the service if they lose their phone. Users must enter a PIN number to access payments through Google Wallet, helping prevent others from making illicit payments with the app.

Though the changes announced Wednesday could increase the commercial viability of Google Wallet, the NFC-based service still faces a significant challenge from the lack of compatible payment terminals at retailers.

A group of 25 national retailers have rolled out NFC payment terminals that work with Google Wallet, and the company's partnership with MasterCard PayPass allows consumers to pay with the app at 200,000 U.S. retail stores.

Even so, NFC payment terminals are far from ubiquitous, limiting the usefulness of the app for everyday consumers.

Google also faces competition from other digital wallets and mobile payment services, as documented in Wireless Week's recent coverage of NFC payments.

AT&T, Verizon and T-Mobile are set to kick off trials of their NFC-based mobile payments joint venture, Isis. There are also a number of non-NFC mobile payment solutions that are already being widely adopted by consumers, such as Square and PayPal's PayPass app.