From Quick Guide: Cellphone Guide
Summary: Activate a used cell phone by visiting your local cell phone service provider, getting a plan and a new SIM card, replacing the SIM card in the back of the phone and powering up the phone. After replacing the SIM card, discover how your new plan should be activated on the used phone with information from the manager of a cell phone store in this free video on cell phones.
Geordie Andurlakis is the store manager at an AT&T Spring cell phone store. He is very knowledgeable with cell phones and has been manager for more than two years.read more
"I'm Geordie, with Spring AT & T, and I'm going to show you how to activate a used cell phone, so first step, is going to your local cell phone service provider. You have to pick a plan, get a number, and get a SIM card, from your cell phone provider. You then take your used cell phone back off, take the battery out, and place the SIM card inside the used cell phone. You then replace the battery, put the back back on, then power on your cell phone. At this time, the cell phone will be tied into the phone number, that you and your representative discussed, and it will work on the cell phone plan, that you chose with your cell phone representative."
eHow Article: How to Activate a Used Cell Phone