Different phones, can't really compare them that accurately. The VZW version is CDMA, those were GSM and different bands than used in the USA. The internals will be tweaked along with the radios, so we will have to see when the Epic and Fascinate get released and reviewed. Even if you could place some blame on the hardware here, or software, our versions are coming a good month or two later. Samsung could easily iron out anything that was reported in Asia and Europe for these phones.
I use to have an Alias, and I loved that phone. Actually, was my favorite phone before picking up an Android phone. So Samsung isn't bad with call quality by default.
On build quality, from the post above, none have said its bad. They just say its more plastic than the X, not that it WILL suffer from it. Time will tell there. Also, judging by the pictures at Androidcentral, the X has some size on it in terms of tallness, there may not be a full inch difference, but I wouldn't call them nearly the same.