Ringtone

A ringtone was a noise made by a mobile phone (or any other form of communications device) to alert the owner to the fact that they had received a call. Said owners had the ability to modify their ringtone to be any sound they so chose.

Examples of ringtones
Petronella Osgood had the "vwoorpy" noise made by the TARDIS' dematerialisation circuit as her ringtone. (AUDIO: United) It was also the ringtone on Kate Stewart's mobile phone to let her know when the Doctor was calling. (TV: The Day of the Doctor)

Dan Hodges had the "Crazy Frog" ringtone on his phone. When Dan's phone rang while Toshiko Sato and Jack Harkness were examining his body, Toshiko mistook the sound as coming from Jack's phone, which Jack took offense to. (TV: Combat)

Flip Jackson had "Pokerface" by Lady Gaga as her ringtone. (AUDIO: The Crimes of Thomas Brewster)

Nobby had the theme tune to The A-Team as his ringtone. (PROSE: Bay of the Dead)

Mephistopheles Arkadian's communicator device played a variation of the iconic default Nokia ringtone. Upon being asked about the sound by Valyes, Arkadian claimed that it was an original composition. (AUDIO: Panacea)

The ringtone on Joe Marquez' PAN played "O, Canada". (PROSE: The Nuclear Option)

Ryan Sinclair's ringtone was the theme music for Fireman Sam. (COMIC: The Power of the Mobox)

Rani Chandra had a Kylie Minogue song as her ringtone (PROSE: Day of the Clown), though according to another account, she instead had a typical phone ringing sound as her ringtone. (TV: The Day of the Clown)

Other references
While possessing Rose Tyler's body, Cassandra briefly mistook the ringtone of Rose's Superphone as originating from her posterior. (TV: New Earth)

The Eighth Doctor once intended to give Lucie Miller a TARDIS key with a musical ringtone as a Christmas present. (AUDIO: Relative Dimensions)

Owen Harper once told Marianne Till that pandemics could "spread faster than Crazy Frog ringtones" if they remained unchecked. (PROSE: Slow Decay)

When first arriving at Deffry Vale High School, the Tenth Doctor thought the students would be happy slapping hoodies with ASBOs and ringtones. (TV: School Reunion)

Behind the scenes
On 26 March 2005, BBC Worldwide released the then-new Doctor Who theme music as a ringtone on the Doctor Who website in Polyphonic or Monophonic formats for WAP-enabled mobiles. The ringtone could be ordered by text or premium-rate hotline and cost around £3. In September 2005, the ringtone was made available in a third format, Real Tone.

As revealed in the Blooper Reel for Series 2 of Torchwood, John Barrowman once had the Doctor Who theme as his ringtone.

Timothy Dalton also once had the Doctor Who theme as his ringtone. Coincidentally, David Tennant's ringtone at the same time was the James Bond theme (with Dalton having previously played James Bond in the films (1987) and  (1989)).