Well after endlessly checking HTC website for the past few weeks Gwyn and Ferjan both simultaneously pinged me emails saying you can now download the Windows Mobile 6 upgrade for the HTC S620 from the HTC E-club.  No word on the announcement page but you can get the download at the URL below:

You need a valid login to do so (using your S620 IMEI number) but can then download the update (which I am now doing - 52% as I type)