Many smartphones operate on newer 3G or LTE networks that offer upgraded security features. But, they still have to interact with the outdated networks that are full of security holes. In fact, the old SS7 network, originally designed in the 1980s, has many flaws that could be used by hackers or governments that want to track or listen in on your calls.
Hackers can use SS7's built-in functions to steal your communication information. For instance, they can request temporary keys through SS7 to unlock calls made through more secure and encrypted networks like 3G.
These vulnerabilities continue to exist even as cellular carriers invest billions of dollars to upgrade to advanced 3G technology aimed, in part, at securing communications against unauthorized eavesdropping. But even as individual carriers harden their systems, they still must communicate with each other over SS7, leaving them open to any of thousands of companies worldwide with access to the network.
Anyone with the right tools and skills can use the SS7 network to track calls, listen in on conversations and steal texts. They can even record encrypted calls and decode them at a later date.