Foreign ownership in T-Mobile US and Verizon Wireless has helped shield the two mobile operators from a controversial data surveillance programme run by the US National Security Agency (NSA), according to the Wall Street Journal (WSJ).

Although NSA doesn’t capture call information directly from T-Mobile US and Verizon Wireless, the report nonetheless points out that the security agency can still collect metadata on 99 per cent of US phone traffic since nearly all calls eventually travel over networks owned by US companies.

The WSJ report, citing unnamed sources, says the two other nationwide wireless carriers in the US – AT&T and Sprint – “have long cooperated with the government”. The NSA, says the newspaper, has standing court orders with AT&T and Sprint for information on all calls over their networks, both domestically and internationally.

Legal, practical and political obstacles are all possible reasons, says the report, as to why T-Mobile US and Verizon Wireless are excluded from the NSA data surveillance program.

Current and former US officials, however, according to the WSJ report, say the likely reasons are tied to overseas ownership. Special court orders sanctioned by the Foreign Intelligence Surveillance Act are classified as ‘top secret’ and ‘noforn’ – short for ‘no foreign’ – which would prohibit some T-Mobile US and Verizon owners from being aware of certain programs.

T-Mobile US, a merger between regional player MetroPCS and T-Mobile USA, is 74 per cent owned by Germany’s Deutsche Telekom. The Vodafone Group from the UK holds a 45 per cent stake in Verizon Wireless.

How far NSA’s collection of call metadata might be hindered by the takeover of Sprint by Japan’s SoftBank is not clear. The Sprint board unanimously approved a revised bid from SoftBank this week that would see the Japanese firm hold a 78 per cent stake in the US operator.

To placate security concerns, Sprint and SoftBank have agreed to a new board-level position of Security Director, which, says WSJ, is likely to be filled by Mike Mullen, a retired US admiral and former chairman of the Joint Chiefs of Staff.

The Committee for Foreign Investment in the United States (CFIUS) approved SoftBank’s acquisition of Sprint last month, an important step for the Japanese company in countering national security concerns raised by its proposed takeover.