Apple says that modification of the phone's software, a process known as jailbreaking, could lead to major network disruptions. Jailbreaking gets around the copyright control features that prohibit, for example, the installation of applications unapproved by Apple.

Jailbreaking continues to be popular with iPhone users, who can also then use their devices on the networks of operators who have not signed distribution deals with Apple.

Apple argues that the practice constitutes copyright infringement. No one has been prosecuted for jailbreaking, although Apple discourages it.

Since the OS code is accessible on a jailbroken phone, Apple said it would be possible to reprogram one to gain access to the phone's BBP (baseband processor), which controls the connection to the operator's network.

"Because jailbreaking makes hacking of the BPP software much easier, jailbreaking affords an avenue for hackers to accomplish a number of undesirable things on the network," the filing said.

By gaining access to the BPP, hackers could change the phone's ECID (exclusive chip identification), which identifies a phone to the transmission towers, Apple said.

"With access to the BBP via jailbreaking, hackers may be able to change the ECID, which in turn can enable phone calls to be made anonymously (this would be desirable to drug dealers, for example) or charges for the calls to be avoided," Apple said.