If you upgrade your iPhone, do they take your old one back?

I upgraded my iPhone about a year ago now and recently I went looking for my old iPhone because I lost all of my contact numbers. But I couldn't find it anywhere. I looked in every room of my house, every drawer, every cupboard, every box. I've spent hours and hours searching for it, but it is nowhere to be seen. I'm wondering if they might have taken it when I upgraded my old one but I can't remember at all. I'm just wondering if anyone else knows if this is possible? Do they take your old phone before giving you the new one if it is an upgrade of the same phone?

No.

When you upgrade, you are purchasing a new phone. You don't have to trade in your old one.

Only just recently have they started doing something like that (The AT&T Next Program, the T-Mobile Jump! Program, etc, require the trading in of your old phone)

But standard, 2 year upgrades, don't require the trading in of your old phone.

I think they do sometimes

No, not unless you intentionally traded it in. Alot do trade them in now though as they give you $ off your new upgrade.