The Xbox consoles never received official keyboard and mouse accessories because of Microsofts refusal to intergrate a keyboard into a Xbox controller, despite continued gamer requests.
But Sony used the keyboard, the PS 2 supported USB keyboard and mice, which will also be seen in the new PS 3.

The QWERTY keypad will be its own separate accessory that will attach neatly to the bottom of the Xbox 360 controller. Its currently unknown exactly how the device will latch on and interface with the controller.
The main purpose of the new QWERTY keypad controller is the rumored addition of Windows Live Messenger functionality into the next Xbox 360 Spring Update.

Release date is mostly in the summer, but pricing is not yet announced.