Don't know if this applies only to me or everyone else too, but:
I just got a text from Verizon thanking me for my recent purchase (obviously my phone). It gave me a promo code to use for an iPhone trade in. For me, they're offering $100 for 4/4s, $200 for 5/5c, $300 for 5s, and up to $400 for a 6/6+.
Sadly, I sent in my 5 for a bill credit about a week and a half ago, so I lucked out and found my old 4 sitting in the drawer that I'll send for $100. It has a small chip in the top of the screen, but shhh, I didn't mention that

lol
So keep your eyes out for a text from Verizon regarding a possible iPhone trade in!