US lawmakers will scrutinise developers that make software for mobile phones, after wireless carriers said that they have no control over them in keeping smartphone users’ locations private.

US lawmakers had asked the wireless companies to explain their policies for handling location data after a report accused Deutsche Telekom of storing detailed location data of a customer for months.

Deutsche Telekom owns T-Mobile USA, but is seeking to sell the company to AT&T.

Four largest wireless carriers in the US — AT&T Wireless, Verizon Wireless, Sprint Nextel and T-Mobile USA – said that they obtain customer permission before using or sharing location data.

In letters to Congress, the carriers said they store the data after taking prior consent and do it to provide driving directions, family-finder applications and other location-based services to users.

However, the companies added that they had no control to force phone makers or independent developers of location-based apps to get similar user consent.

The letters were released when Apple, Google and Microsoft are embroiled in a controversy regarding tracking user movements.

In response to the letters, the lawmaker expressed "uneasiness" about how data collected by wireless carriers may be used by other companies.

"After thoroughly reviewing the responses from the wireless carriers, I am left with a feeling of uneasiness and uncertainty," Texas Republican and Representative Joe Barton said.

"The companies informed us that customer consent before access of location data is a common practice, but the disconnect is when third-party applications come in to play … It is time we hold third-party developers accountable, and I am determined to work with other members of Congress to get this done."