Der Spiegel has reported that it has obtained National Security Agency (NSA) documents in which the agency states it accessed data from Apple iPhones, BlackBerry devices, and phones that use Google's Android operating system.
Der Spiegel said most smartphone data can be extracted, including users' contact lists, text message logs, and information on geographical locations.
The NSA had set up working parties to ensure that each of the main operating systems had a "back door" accessible to spies, the magazine said. Critics warned that hackers may one day discover the NSA's "back doors" and exploit them for crime.
Information leaked this year by former NSA contractor Edward Snowden that shed light on the extent of US electronic surveillance has sparked international outrage.
In Germany, it has stirred memories of totalitarianism, still raw 68 years after the Nazis and the communist era.
Canada-based BlackBerry, which has sold its devices to many governments by advertising that the encryption is too strong for anyone to crack, could be commercially affected if it is proved that a weakness does exist.
Der Spiegel said the NSA is able to penetrate iPhone data via the owner's personal computer after their data had been synchronised.
On Saturday, the latest protest against US spying in Germany drew at least 10,000 participants to Berlin.
It came after reports that software companies using Secure Sockets Layer (SSL) technology, employed worldwide in browsers for online commerce and in corporate networks, had been induced to install "back doors", sometimes knowingly and sometimes without realising it.
Der Spiegel is expected to release the documents on Monday.