Mobile phone

Mobile phones are handheld mobile communication devices originating on the planet Earth, they became prominent amongst much of the population in the early 21st century.

Both Rose Tyler and Martha Jones had their mobiles adjusted by the Doctor (Ninth and Tenth Doctors respectively) to have 'Universal Roaming'. (DW: The End of the World, 42)

Anji Kapoor carried her mobile with her when she began travelling with the Doctor, and was even able to use it when she travelled into her future. (EDA: Escape Velocity, Trading Futures)

The Eighth Doctor also set up mobile phone-like devices for Ani and Fitz Kreiner when they spent a selective amount of time on certain planets. (EDA: The Book of the Still)

Sarah Jane Smith, Josh Townsend and Natalie and their respective friends frequently used mobile phones to keep in regular contact with one another. (BFA: Sarah Jane Smith (audio series))