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Wireless is a Colonial term used to describe short- to medium-range electromagnetic communications from ship to ship, or ship to planet. The term is also used as a noun to describe the device used to pick up wireless broadcasts, such as a "shortwave wireless."
Wireless appears to work using frequencies available from a similar electromagnetic spectrum as used on the Earth we live on today. Shortwave transmissions exist in the Colonial wireless spectrum (Miniseries). With this similarity, wireless is limited in range based on other celestial bodies, antenna direction, nuclear and other man-made EM interference, distance (where the time to send or receive a message might be measured in minutes and not fractions of a second), and broadcast reception or transmission limits of the vehicles in communication. A Raptor, for instance, may be able to hear transmissions from its mother ship, Galactica, but may be too far away to return a reply as it may not have as strong a wireless transceiver than Galactica to push the message.
Sharon Valerii uses a communication drone to extend her Raptor's transmission range in principle after her ship leaves Caprica with several refugees during the Cylon Attack (Miniseries). The drone contains an automated distress call with its own wireless transmitter. She uses to the probe in hopes of transmitting her call for help outside of the Cylon fleet, which were jamming many Colonial communication channels.
Emergency wireless handsets are included with a Viper pilot's emergency ejection survival kit. Unfortunately for Starbuck, her handset is smashed on her parachute landing on a desolate moon, forcing her to seek alternate means to return to the Fleet (You Can't Go Home Again).
On advanced battlestars, wireless communication between CIC and other departments of the ship may likely be the standard mode of communication. On ships such as Galactica, however, communication is done through hardwired phones and public-address systems per Commander Adama's orders that no networked computers (including communication computers) be used on board to avoid Cylon infiltration.