SmartWatchM for Sony Ericsson BT watches is a notification utility, running on your Windows Mobile Smartphone, which uses the Sony Ericsson AT Commands over Serial Port Profile to connect to Sony Ericsson and other Bluetooth watches to provide text and picture notifications on the watch itself, much like the dearly departed Microsoft Spot system, but much better. It supports all main features of Sony Ericsson phones and it even has some extra functions.
The watch-phone combination supports features such as SMS notification, Appointments, Missed call notification, Caller ID, Music player control, setting the time of the watch from the phone and many many more functions.
The software is currently compatible with MBW-200, MBW-150 (Music, Classic, Exclusive), MBW-100, and Abacus Caller ID Watches (the last two may not support all features). The MBW-150/200 is recommend you do not have a BT watch already.
Read more and download the software from this XDA-Developer thread here.