It depends. Most wireless carriers offer trade-in programs to help consumers defray the cost of a new phone. However, trade-in programs are often linked to contract requirements, so while you may get a discount on a new phone from your trade-in, you’ll be obligated to stay with the carrier for up to two years. Selling an old phone to pay for a new one is usually a good idea, but if you want to maximize the money you receive, sell your phone privately. Carriers rarely offer top dollar for used phones.