Sony hasn't had much success with the US market so far. They tried to make it big last year with the Xperia Play, the gaming smartphone that featured an embedded controller, by launching it on Verizon, but unfortunately for them, the sales weren't that great. The reason for that was because the Xperia Play came with outdated hardware, and the whole concept might not have been the greatest idea over, or if it was, Sony didn't implement it properly.
I don't think Verizon was too happy with that, and they haven't gotten that much support from other carriers since then either, at least until AT&T got the Sony Xperia Ion (basically an ), but that, too, came too late to market in US, but this time it's very possible it was AT&T's fault who would rather force Sony to redesign the phone for them, and delay it for a few months, than get the same version.
So now Sony is changing the strategy a bit, and is planning to release 3 of its best smartphones, for different price ranges, as unlocked: Xperia S for $600, Xperia P for $480, and Xperia U for $300. The US is not exactly a country known for people buying their phones unlocked, especially for such high prices, mostly because the carriers both promote the subsidized version more, but also don't give you much of a choice either, because there's usually little to no difference between a plan that subsidizes your phone, and one that doesn't. This might make Sony's sales in US pretty low, but at least it's better than nothing, and they get their foot in the door.
The more disappointing thing about the Xperia P and Xperia U is that they are still arriving with Gingerbread, which will even make those slow sales even slower. The 2 phones will probably get Android 4.0 down the line, but no timeline has been given for that. So this begs the question, do you buy a $600 Xperia S phone with Android 4.0, or its hardware equivalent, the Galaxy Nexus, that now comes with Android 4.1 and costs only $350 unlocked, which is just $50 more than Sony's low-end Xperia S phone?