Communicator

The communicator was an aptly-named device given to Amy Pond and Rory Williams on their honeymoon by the Eleventh Doctor, for the latter to tell the married couple when he was coming to collect them. Instead, Amy used it to contact the Doctor when the Thrasymachus was crashing into Ember. (TV: A Christmas Carol)

In the Federation universe, all Starfleet personnel had communicators. In the 23rd century, communicators were styled like smart phones and had a gold cover, the Fourth Doctor making use of James T. Kirk's to defeat a group of CyberNomads. In the 24th century, the communicators were known as combadges and affixed to the chest of officers. (COMIC: Assimilation²)