Eavesdropping just got way easier, as according to German computer scientist Karsten Nohl GSM security used to encrypt calls was "inadequate."
For the past five months, Karsten Nohl along with other experts was working on hacking the encryption algorithm used on GSM networks.
The resulting security gap could allow criminals and lawbreakers to eavesdrop on private conversations of 4 billion cell phone users around the world.
At the Chaos Communication Congress in Berlin Mr Nohl expressed concern about the widespread vulnerability users are currently facing.
"We hope to create some additional pressure and demand from customers for better encryption." said Mr Nohl.
GSM Association (GSMA), which has developed the algorithm, has termed Mr.Nohl's work as "highly illegal" UK and other countries.
Along with a few experts, Mr.Nohl has published materials that would crack the A5/1 algorithm, the most common one used on GSM networks.
Decrypting GSM calls and listening to calls was possible earlier but would cost thousands of dollars.
Experts are worried about Nohl's findings, as cracking GSM calls would now become easier and accessible to technologically literate criminals.
GSMA wrote off worries by saying that "reports of an imminent GSM eavesdropping capability are common".
The association also said that a new proposal to upgrade the current A5/1 algorithm to a new standard called A5/3 is being sketched out.
Photo Credit: AP/Shizuo Kambayashi