I don't think the sticker over the main display telling the customer the best place to hold the phone is out of line in any way! The tag is not saying that you're not gonna get signal or the phone will be innoperable if you hold it wrong. Its simply saying you'll probly get slightly better performance. And lastly THIS IS NOTHING NEW!(At least not to be complaining about it now) This sticker appears on most new Sprint phones including some with external antennas.
Honestly we're gonna call this a "con" about the phone. Its the thinnest phone in the country! I'm not a phone designer or anything but I would assume things have to be placed pretty strategicly in these things!