Oh, I double this request!
I do own an MBW-150 and I contributed as much as I could over at xda-developers.com (kinda like the same what this forum is but for HTC devices) in the developement thread of SmartWatchM, the software by www.smartmadsoft.com

shadowjk, Sony Ericsson claims that the watch does AVRCP, but it doesnt, it doesnt follow the standard at all. Some guys at xda-developers.com figured out how the watch connects and got it to work. The result is BTWach (or so I think, obsolete by now) and SmartWatchM. The watch is quite powerful once you figured out how it works. It is even possible to send pictures to the phone or create "complex" graphical menues on the watches display to remote control the phone it is connected to.

Anyone interested might get in touch with the guy behind SmartWatchM. Shouldnt be a problem to port the necessary parts onto Maemo...