Seems Omnia i900 users are in luck. A customer who contacted Samsung Netherlands got the following reply when he asked about the Windows Mobile 6.5 update.
In your email you ask the question if windows mobile 6.5 will be released for the Omnia. We can confirm that this is coming, however the exact release date isn’t known yet, we therefore advice you to keep an eye on www.samsungmobile.com.
This acknowledgement is a bit surprising because the general trend among handset manufacturers is to limit support for older handsets so that users upgrade to a latest one but this looks to be a good move to extend the original Omnia’s longevity.
There’s no word on the firmware price too but I guess it won’t be paid one.