Panasonic, Seimens, Braun, GE, and a few others have 2-way/multi-handset models, too. Here at Timberland, we use the 2.4GHz Panasonic setup, with the base unit/speakerphone in the kitchen, and handsets scattered throughout the house ... generally, however, never in the same location as the person getting the phonecall
The system works pretty well, actually, and we even use it as a floor-to-floor, room-to-room, or house-to-outbuilding intercom ... as long as its remembered to bring a handset along. Theres a big brass bell hangin' outside the back door that still gets used though ... hear the bell, come to where you can shout back-and-forth with whoever's at the house