this is how mobile networks can upgrade to make surveillance more difficult
"Wireless carrier T-Mobile US has been quietly upgrading its network in a way that makes it harder for surveillance equipment to eavesdrop on calls and monitor texts, even on the company’s legacy system.
The upgrade involves switching to a new encryption standard, called A5/3, that is harder to crack than older forms of encryption. Testing by The Washington Post has found T-Mobile networks using A5/3 in New York, Washington and Boulder, Colorado, instead of the older A5/1 that long has been standard for second-generation (2G) GSM networks in the United States. More advanced technologies, such as 3G and 4G, already use stronger encryption