First check if it is the phone or the line. Try replacing the cables. Use another phone (known working) to see if the jack has a dial tone with it. If you have dial tone on another phone and not on this phone with any set of RJ-11 cords, then send the phone to AT&T for repair. It had a 1 year warranty. Contact the customer service at www.telephones.att.com
, or call 1 800 222-3111.
Try both phone on other jacks with that line, if available. If the phones work on other jacks but not on the first one, open up the faceplate and check for loose wires. Most either use screws to hold the wires or have keystones with punch downs. If you have the screw type, strip the wire strand if needed and resecure the wire. http://www.lanshack.com/wire_phone_jack.aspx
has the diagram of the wiring. The keystone punchdown tool is available at stores like Lowes and Home Depot, among others - in the section for wiring a new home.
Try then on another line, if possible. If the phones work here, then it is a general wiring issue on the other line.
Find where your telephone service comes in and see if the box has RJ-11 connections. Try your phones there. If the phones do not work at other jacks and the service connection is not RJ-11, call your telephone provider. They can test the line and will repair the line free if it is an outside issue. If the issue is inside, check all exposed wiring for damage. Check the jacks as well. If it is a problem inside the wall, you may want a professional. Your telephone service provider will probably fix it for a fee.
I hope this helps.