I think this video will answer your questions about the Ozone on gsm.
http://www.youtube.com/watch?v=lXBx32Ui1rw
Omnia also has a better camera with flash. Also has 8/16gb of onboard memory, has one heck of a kickass speaker for music/speakerphone, and a larger, better screen for reading texts/emails. but no hardware keyboard. If you dont' mind going touchscreen only, then it's a really nice phone to have.
My suggestion is go down to a store that has working models of both and play around with them.
A lot of people don't like the stock keyboard on the Omnia, myself included. Just keep in mind that you can change that out with a 3rd party keyboard. THe one from SPB is very popular. And it's not AS bad, once you properly configure the touchscreen.
I can't speak for the Ozone, but if you're in an area with spotty signals, the omnia will drain the battery FAST. I go to tech school for 5 hours a day, and the training room is on the bottom floor of a 3 story mall. Reception is BAD, especially with all the electrical interference from all the computers, cables, and servers. So it's trying to locate a signal about 45% of the time I'm in class, and can suck my battery down anywhere from 30-60%.