Google launches its mobile network:

 Project Fi to bring cheaper calls and texts to the US

Google is already the world’s most popular phone software provider, and a pay-TV operator - and now it wants to be your mobile network carrier.

The company has unveiled a U.S. wireless service that switches between Wi-Fi and cellular networks to curb data use and keep phone bills low.

The service, called 'Project Fi,' debuted today, about two months after Google revealed its plans to expand its ever-growing empire into providing wireless connections for smartphones.

Google is selling the basic phone service for $20 a month and will only charge customers for the amount of cellular data that they use each month, instead of a flat rate.  

Each gigabyte of data will cost $10 a month. That means a customer could sign up for a plan offering three gigabytes of data and get $20 back if only one gigabyte was used in a month.

Most wireless phone carriers allow their customers to roll over unused data into another month of service without refunding any money.

Project Wi-Fi initially will only be sold to a narrow US audience that owns the Nexus 6, a smartphone that Motorola Mobility made with Google's help.

Google's pricing setup makes Project Fi less expensive than most of the comparable plans offering by the four biggest wireless phone carriers - Verizon, AT&T, T-Mobile and Sprint. 

The monthly prices for a single line of smartphone service with up to one gigabyte of cellular data at those carriers range from $45 to $50 compared to $30 from Google.

The major carriers, though, offer a variety of family plans that could still be better deals than Project Fi. Those bundled plans allow several phone lines to share a pool of cellular data.