There are also the sort-of television screens Turaga Dume used in Metru Nui, which appeared to be able to show live video (at least within the coliseum). To me that would suggest long range communication is at least possible, in theory. I imagine the way the MU was initially designed, long range communication just wasn't something the Great Beings felt was needed. The domes might also restrict a lot of long range signals anyway, but that's just conjecture on my part.
Sidenote: I vaguely remember the screens on Metru Nui as being described to be similar to a real world type of display (I can't remember what it was called, but you can search "coca cola kinetic display" because it looked something like that). If Bionicle was going to have an equivalent to TV screens I honestly imagine it would something like that.