A "Lookup" is a handheld, personal device that everyone has in the Portal Future world. These devices can be a basic model to a luxurious one with all of the bells and whistle.
A lookup is both a calling system, a computer and used for entertainment all in one; and small enough to fit in a pocket. They are also a holo projector so when talking to someone, the other persons image, in real time, can be projector against any kind of backdrop or entertainment shows can be projector and viewed in 3D.
|In the Portal Future, core mail addresses are very unintelligible strings of numbers, but people can link them to much more memorable user names. The equivalent of customized ringtones are available but people rarely bother with them because lookups usually flash up caller images. Spambots, fraudsters, and scam callers aren’t a problem in 2789, partly because of comms portal twinning making it easy to trace calls back to their source, and partly because they’re dealt with by specialist cross-sector units so can’t hide behind the equivalent of borders.|
–Janet Edwards Q&A, 
A Military lookup is curved and attaches to the forearm of either an impact suit or the military uniform, so it is easily accessible and secure.
Some of the military lookup's have built in security features that prevent conversations from being overheard.