This is an interesting like I came across! http://www.pspmyspace.com/omnia/2008/09/how-to-hard-res.html
My omnia hangs now and then for the past few days. Dont know why. I decided to do one hard reset once. I am okay with the loss as Google Sync takes care of all my contacts and mails.
There are couple ways mentioned in the page I quoted above! I tried the second one
Typing the above will reset the phone, and restart it couple of times to ensure the factory settings.. (I doubt, I saw some internet profiles, menu items were still there!!!)