From Verizon's site (see the part in red I highlighted):
Purchase the iPhone 7 or 7 Plus on Device Payment and trade in a smartphone for up to $650.
- iPhone 6, 6 Plus, 6S, 6S Plus for $650
- iPhone 5, 5S, 5C, SE for $400
- HTC One M9, LG G4 or V10, Samsung Galaxy S6, S6 edge, S6 edge+ or Note 5 for $300
- Droid Maxx 2 or Turbo 2, HTC One M8, LG G3, Samsung Galaxy S5 or Note 4 for $200
- Droid Maxx or Turbo, HTC One M7, LG G2, Samsung Galaxy S4 for $100
Trade must be in good working and cosmetic condition. New iPhone 7 / 7 Plus promotional trade-in credits issued over 24 months and will appear in 2-3 bill cycles after trade. Smartphone purchase must be made in a Verizon Wireless retail store or on
www.verizonwireless.com.
Your iPhone 7 / 7 Plus must remain active on a device payment agreement for 24 months to receive credits. If you cancel service, or if device payment agreement is paid off or transferred, trade-in promotional credits will stop. Limited time offer.