US number-two operator AT&T expects to close its 2G GSM networks by 2017 at the latest as customers are moved to its 3G and LTE networks.

"We expect to fully discontinue service on our 2G networks by approximately 1 January 2017," the company said in a filing with the US Securities and Exchange Commission. It added that just 12 percent of its postpaid customers were using 2G-only devices at the end of June 2012.

AT&T said it is facing significant spectrum and capacity constraints on its wireless networks and, with demand expected to increase, plans to redeploy 2G spectrum for 3G and LTE services.

This upgrade process will take place over a number of years during which the company aims to minimise customer churn and will evaluate the financial impact of moving 2G customers onto 3G and 4G services. An AT&T spokesman told the Wall Street Journal that 2G-only handsets are no longer sold by the operator.

AT&T started to roll out its LTE technology in September 2011, and its networks now cover more than 74 million people in 51 markets. The company  last week announced plans to acquire wireless technology company NextWave Wireless for up to US$600 million to add to the spectrum it holds.