I've searched enough to know that this isn't a huge surprise, but I've put enough effort into it that I thought it might be worth recording for others.
The SMT-5800 is a smartphone running windows mobile 6 (or CE OS 5.2.1238). I was happy to connect it via Bluetooth to my QSTARZ BT-1200 Ultra GPS logger using serial port COM0 in the Bluetooth setup. I can use BeeLineGPS to interact with it.