Sub-wave communication
From Tardis Wiki, the free Doctor Who reference
A sub-wave communnication is a form of communication that can be undetectable to Dalek scanners. The wave was used by Harriet Jones, Martha Jones, Captain Jack Harkness and Sarah Jane Smith, with Rose Tyler only watching. The signal was used to combines the enitre Earth's mobile phone signals to communicate with the Doctor by using the rift in time and space, which was used to contact the TARDIS to Earth's location when the planet was stolen. (DW: The Stolen Earth)
