Ericsson made some interesting accessories for the T28, like the "CHA-10 Chatboard" (a QWERTY keyboard for text messaging), the "MP3 hands-free kit HPM-10" (an MP3 player with an MMC card slot and standard 3.5mm headphone jack) and the aforementioned "Bluetooth phone adapter DBA-10".
The MEX-BT5000 acts as a hands free kit for any Bluetooth phone (although we're sure they'd prefer if it was one of their own), giving you access to up to 50 of your contacts and six of your speed dial entries through its "high resolution" screen and integrated noise-reducing micophone.