Generally what they do is if they have one that's refurbished or new they will send you that phone. If they don't make it anymore they can not give you a phone that's less than what you paid for. So for example lets say they made 3 chocolates [I believe there's only two but this is an example] If you bought the 2nd one they came out with, which is better than the first, but not quite as great as the third they came out with, and the second one broke. If they stopped making the second, they can not give you the first chocolate they made as a replacement, because you paid a certain price for your phone and you have to get something of equal of greater value back. So they would have to send you the 3rd chocolate they came out with.
So you'll be getting a better phone than what you had if yours is not in stock. Whatever the LG glimmer upgrade is, you will receive. I'm not sure I would call and ask, but they can not give you a phone of lesser value. The same thing when your phone breaks by itself, I have the blackberry curve. The next upgrade for the curve is the storm. My phone has had malfunctions by itself, I've had 2 replacements done on it, and if I have a problem with the one I just received I get a free upgrade to the storm because of the inconvenience I've already had.