If i upgrade to iPhone 5 how long til I can downgrade?

I really like my current phone and want to buy the new iPhone 5 but not yet use it… Maybe in a couple of months. I'm eligible for an upgrade. So can I downgrade to my old phone the same day I activate the iPhone 5?

Most cell carriers just maintain your account once your contract term runs out, so you'll still be eligible for an upgrade in a couple months - and after Christmas, you'll actually be able to buy an iPhone 5, instead of just ordering one.