First, make sure everyone in the group has each others' numbers and start a group text. Then, one person hides an item somewhere in the house. Next, the person who hides the prize sends out hints, one at a time, and leaves a lag time between texts of about two minutes. Every two minutes, a new text hint is sent out by the hider until the prize is ultimately found. The winner becomes the new hider.
This may not get them off the cellphones, but at least it is interactive and can actually start a real conversation!