Mobile phone

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

Rose Tyler, Martha Jones and Donna Noble had their mobiles adjusted by the Doctor (Ninth and Tenth Doctors respectively) to have 'Universal Roaming'. These became known as Superphones as they were able to call anywhere in time and space and could apparently work in areas of no service such as the Cabinet Room. The Doctor also modified Barcly's phone in this manner, but he did it so he could communicate with UNIT. It is unknown what he did with this phone afterwards, if he undid the Universal Roming and gave it back, just gave it back as is, or kept it. (DW: The End of the World, 42,The Doctor's Daughter)

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))