For starters, shop around for the best buy back price.
Big Box retailers like Best Buy, Amazon, and GameStop all have buy back programs, as do the wireless carriers.
But also look out for services that solely focus on trade-ins, like Gazelle or ecoATM.
Not all services offer the same prices, so do some comparison shopping to find the one with the best offer.
While you're there, find out exactly how you'll be paid.
Retailers usually give you in store gift cards while other services will give you cash or check.
Bottom line, read the fine print.
When you give away your phone, even to a carrier buyback program, you won't be able to get it back if something goes wrong.
And finally, consider donating your old phone.
Charities like Hope Phones and Cell Phones for Soldiers let you hand off your phone to someone who needs it.
In San Francisco, I'm Sharon Profis, CNN.com for CBS news.