Google is preparing to sell mobile phone plans directly to customers and manage their calls and mobile data over a cellular network, according to three people with knowledge of the plans.

The new service is expected run on Sprint and T-Mobile’s networks, two people familiar with the product say. Google is expected to reach deals to buy wholesale access to those carriers’ mobile voice and data networks, making it a mobile virtual network operator, or MVNO, they say.

Codenamed “Nova,” the project is led by longtime Google executive Nick Fox. A launch this year seems likely. Mr. Fox had previously looked at starting the service last fall, and some employees have already tested it.