Upgrade Elgibility comes after the 20th month of a 24 month contract. Make sure that your contract itself is up 12/24/09 rather than your UE date. You should be able to check on My Verizon if you are elgible.
I know that with Alltel and doing an Exchange by Mail, you could request to get a different phone after the 4th one if it was a recurring problem. I am not sure how it works with Verizon. They might be willing to let you do an early upgrade if you upgrade to a VZW device and plan
The other thing I think is that if you have any other lines on your plan that are elgible, you might be able to upgrade all the lines.