The Samsung Omnia is only available as an unlocked import in the United States for now. MobileTechReview has published a Samsung Omnia (I900) review with lots of screenshots and a video.
Quote from the review: "We tested the phone with AT&T and T-Mobile US SIM cards, and the phone worked fine with both. We have the Singapore model and it lacks data and MMS auto-configuration for carriers outside that region. So you'll have to enter your carrier's data and MMS settings manually.
The phone's web browsing experience is superb when on WiFi (HSDPA would be lovely too, I'm sure)."
Read the full review on MobileTechReview.
Engadget Mobile also published a review of an import Samsung Omnia.
See also this fun Samsung made viral unboxing video of the Samsung Omnia.