We recently took a look at the Xbox 360 Messenger Kit, which includes a chatpad that snaps into the bottom of an Xbox 360 controller. While the chatpad was released over a year ago, the PS3 keypad just saw a release in Decemeber of 2008. While it does suffer from a few functional omissions and ergonomic irritations, the PS3 Wireless Keypad is the best way to chat with friends and browse the Internet on the PS3.
Unlike the chatpad, the PS3 keypad does not electronically connect to your Sixaxis or DualShock 3 controller. Instead, the pad is fitted with a retractable clamp that attaches to the controller. This not only means that the keypad requires a separate battery charge, but it also will need to be paired independently from the controller itself. You'll need a USB cable (not provided) to initially set up the device and pair it to your PS3. You'll also need it for charging the internal battery.
The keypad is small, and its buttons are very cluttered. We'd imagine people with thicker fingers will have a hard time typing away on it. During our testing, we found the QWERTY keys responsive and we liked how the buttons are angled like a conventional laptop or desktop keyboard. When connected to your controller, the keypad rests raised and above the L and R buttons. While the pad doesn't affect gameplay at all, you will find it a bit awkward trying to reach the keys when it is time to type--you'll basically have to regrip the controller from the top. We found removing the pad altogether from the controller led to a more comfortable typing experience.