"Is there a telephone or a tablet here?" would be "Finnes det en telefon eller et nettbrett her?" or "Er det det en telefon eller et nettbrett her?"
In this case, "det" points to the object that the speaker is looking at, and the norwegian sentence is about discerning the nature of the object in question, not about determining the existence/non-existence of one.
Hi Linn, along that line, most of the time we'll (Am Eng speaker) use "phone" in lieu of "telephone". Is "fon" used in Norway? 12Jul17
No, Norwegians feel no need to shorten "telefon", but as the fox said we do shorten "mobiltelefon" into just "mobil".
Is "tablet" (the swallowed medical capsule) also nettbrett or is that a different word?
Different word (if you break "nettbrett" down the literal translation is "internet board"):
en tablett = a tablet
en/ei pille = a pill
en kapsel = a capsule