Cisco to ship Wi-Fi cordless phone in June: The Cisco phone requires some kind of PBX (phone exchange), but it's unclear from any of the articles I've read whether there's a gateway box you need to interface with specific PBX models.
Cisco might later release a version of the phone that does Wi-Fi in the enterprise and cell flavors when roaming.
It talks to a Cisco PBX, of course.
True Wi-fi Phones, where to buy