I just got an Audiovox SMT 5600. I’ve got it running Windows Mobile 5 and here’s how I did it.
First I hit thepiratebay.com, searched for “windows mobile 5” and downloaded Windows.Mobile.5.ROM.Pack.For.HTC.Typhoon.C500.SMT5600. The nfo file contains instructions for flashing the ROM however mine came with the latest Smartphone 2003 image and could not be upgraded. So I used a post at modaco.com to start the down-grade process. This article provides a link to an Orange ROM which was still too new to perform the Mobile 5 upgrade so I followed this article at mobismart.net to downgrade further to a 1.0 image. At this point I was able to reflash up to the Mobile 5 image successfully.
So far I have not found any software that works with this version but I’ll keep you posted.