To change your AT&T cell phone number, call AT&T customer service, or go online to the AT&T Answer Center where you can find detailed instructions and links to the appropriate webpages. There is a fee associated with a phone number change. You can find more information here: www.wireless.att.com
You can change your AT&T phone number by contacting the company. There may be a $35 charge. Sometimes you can get the charge waived. Talk with an customer representative, they will be able to help you.