You can purchase a new phone directly from a carrier store, but if you're not sure what to buy, we recommend going to a third-party retailer. Best Buy, RadioShack, Target, and Walmart all sell phones, as well as carrier plans. A big advantage of buying a phone or a tablet from a third-party seller is that you have dozens of phones from multiple carriers at your disposal. If your contract is up and you're trying to choose between the iPhone 4 (AT&T) and the T-Mobile MyTouch 4G, for instance, you can compare the two phones side by side in the store. You can't do the same at a carrier store, because those phones are on different networks.
If you're considering buying a phone as a gift, definitely consult with the recipient before you go shopping--and although it will ruin the surprise, you'll probably want to bring them along on your shopping trip. We recommend getting as much hands-on time as possible with multiple phones before settling on one.
Shopping for a new plan? Be completely realistic about how you will use your phone. The national phone plans that the major carriers offer will let you send and receive calls anywhere in the United States (and even in parts of Canada) at no extra charge. You may be able to sign up for a local or regional plan that limits the areas where you can originate a call and still pull from your monthly pool of minutes; this option might be worth considering if you use your phone for local calls exclusively. If you have a world phone and plan to use it in other countries, choose service with international roaming.
When selecting a plan, it's best to overestimate the number of minutes you'll be using for every sent and received call. Because one carrier's definition of off-peak may be different from another's, ask the carrier to specify the times for its peak, off-peak, and weekend hours. Other service charges include those for a data plan, three-way calling, and downloads.
In particular, take into account your data usage (e-mail, photos, IM, and Web access) when picking your cell phone plan. Most carriers bundle voice and data plans together, while others let you select a voice plan and a data plan separately. You can always pay for messaging and data use à la carte, but you'll likely be charged a higher rate. If you think you'll be sending and receiving data with your phone, select some sort of data plan.
When dealing with store representatives, ask them to be as straightforward as possible. Tell them exactly what you're looking for and what phone or plan will fit your requirements. If you're completely unsure, ask them what phone they use, or which phones impressed them this year. Don't let them jump into a corporate spiel, or else you'll end up spending way too much time in the store. And remember, they're human beings too, and they're working during the holiday rush--be courteous, and you'll receive the same treatment in return.
Lastly, familiarize yourself with the store's return policy--especially if you're buying a phone as a gift.