What it means is that there's a probably a book, and when I say book I mean most likely a phone book sized document, of tests that need to be run on the phone in order to be "verified" for use on the network. They get a number of handsets and run them through the tests in a lab environment, which can be anything from a test engineer's desk to a specifically designed room with a whole host of equipment, checking the actual results against the expected results as defined within the test documentation. From things as simple as "turn on the phone and verify it finds a cell phone tower" to "verify operation of a 4G cell call while accessing the internet simultaneously receiving a text messages during a tower handoff", they will basically try to cover what situations could cause either the phone to flip out or the phone to affect operation of the network. Each test will be documented down to the individual steps (Step 1 - Power the device on. Step 2 - Verify that the phone OS load properly. Step 3 - on test station XYZ verify that phone has broadcast signal with X parameters. Step 4 - Verify that test station XYZ running tower simulation 13a59x acknowledges receipt of initial broadcast from Step 3), and each of those will need to be performed, witnessed, and signed off.
The trouble is...if what I wrote above sounds tedious that's pretty much the sexy-glam description. So you've got a Twinkie-eating cubicle dweller who has to run the tests whilst trying to remain motivated enough not to decide between unemployment and workplace violence. If the results are wrong he has to document that and then flow it up the chain for a whole bunch of meetings and an eventual response published to the handset maker. If they're right, then he has to document it and flow it up the chain so he can eventually do it all over again while being hawked on by an underpaid, over-egoed senior/supervisor. And hoping there isn't some sort of fluke in the hardware or lab environment that doesn't cause the test to fail then. Not a lot of motivation to get jumping on things is there....
Plus, as someone else said....for AT&T the flagship phone's now the 1020. The 920's got one foot in the grave at this point, so where is the priority? They'd much rather have you use that nice juicy upgrade, or do a line-swap upgrade to get you into the latest and greatest phone that comes already full of that GDR2/Amber goodness (pay no attention to the 2 year contract extension behind the fine print!).