Finally Sony Ericsson released MR1 for the K790i on FOTA. Here's the update process. It took about fifteen minutes from start to end.
Searching for update
This screen repeats itself after the next one and I snapped the pic the second time, that's why the clock is out of order
Data traffic is charged according to your service. Do you want to download the latest software updates to your phone? Size: 3282 kB. Continue? Yes/No
Downloading update
The phone will restart and cannot be used during the update. Update now? Yes/No
Beginning update
This step took a few minutes
This step took the longest, probably close to 10 minutes
This step only took a few minutes
A new version of the software has been installed. Sending status to the server. Continue
Current software version