In the VZW CES keynote, one of the three big wigs who answered questions at the end stated flat out that you could put a SIM in from any wireless company (yes even AT&T) and have the phone work on their network. It will not work on Sprint as they are also CDMA but as you should already know VZW and Sprint CDMA phones cannot be used back and forth. But you'd be able to move the Bionic to AT&T or T-Mobile.
I caught this too. I just listened to the response again ([video=youtube;DpW0VSSifkw]http://www.youtube.com/watch?v=DpW0VSSifkw]YouTube - Verizon Wireless Q&A Segment at CES[/video], at the 3:30 mark). I did some more research and it seems LTE SIM cards have more "security" features than GSM SIM cards. One of these features could be used to allow the vendor to remotely lock/unlock access to other bands. No doubt that will come into play.
I don't think VZW wants their devices running on other US bands. But for global, it looks like as long as you activate it in the US once (so it's in VZW's system), they'll be glad to hook you up with global GSM (and LTE as available) bands.
Just to note, AT&T and T-Mobile are global wireless carriers. Out of the US, T-Mobile has a much larger footprint, but I think AT&T is in Canada as well.
This will 100% roam globally, and I am not yet willing to concede the inability to switch to another carrier in the US. While this phone is being launched on VZW, it is Motorola's phone not VZW's.
I am certain you could find one on eBay and probably run it on T-Mobile, but of course the question would then be ..... why on earth would anyone in their right mind want to?