At the dinner table, both Marty Jr. and Marlene have VR goggles. Marty wears his continuously, but Marlene is more polite and rests hers around her neck when with the family. When she receives a call, red LEDs flash the word PHONE on the outside of the goggles as they ring. This would be a useful signal if the volume were turned down or the volume was baffled by ambient sounds.
Marty Jr’s goggles are on, and he announces to Marty Sr. that the phone is for him and that its Needles.
This implies a complete wireless caller ID system (which had only just been released to market in the United States the year before the movie was released) and a single number for the household that is distributed amongst multiple communications devices simultaneously, which was not available at the time (or hey, even now), so it’s quite forward looking. Additionally, it lets the whole social circle help manage communication requests, even if it sacrifices a bit of privacy.