SAN FRANCISCO (Bloomberg) - Google Inc. is set to unveil its planned U.S. mobile-phone service as early as Wednesday, and is expected to let customers pay only for data they use every month, the Wall Street Journal reported, citing people familiar with the matter.

Last month, the world's largest Internet-search company said it was planning to offer a wireless service on a limited basis, without giving details on the timing. Google's service will run on Sprint Corp. and T-Mobile US Inc. networks, the Journal reported, and the service initially will work only on Google's latest Nexus 6 phones. A Google representative declined to comment.

Selling its own mobile-phone service could enable Google to add users for its Android operating system, used by many different device makers, and make it easier to serve those users advertisements via smartphones and tablets.

At Mobile World Congress in Barcelona in March, Google Senior Vice President Sundar Pichai said Google was working with mobile carriers to "push the boundaries" of data services in the U.S. The initiative will be on a small scale, he said.

Google is investing more in mobile software and services as consumers increasingly access the Internet and digital features through wireless devices. Android dominates the smartphone industry, with more than 75 per cent of the market, according to researcher IDC.