The phone doesn't have an answering system built-in. If you use a voicemail service, you will need to check with the provider for the phone number and then follow their directions to set up your mailbox. If you are connecting a stand-alone answering machine, you will need to daisy chain the devices. Connect the phone cord from the wall jack to the answering machine IN port. Then use another phone cord from the answering machine OUT to the CL2909 TEL port. (If you are using a fax modem (or regular modem), with an anwering machine feature on your computer, then you still want to use this chain method. The data port may not let the computer answer a voice call.)
If you are using a free standing answering machine, after connecting everything together, make sure that you hear a dial tone and can properly make calls. If you do not get a dial tone, replace cables. (I recommend you check that the phone works by plugging it directly to the wall jack before doing a daisy chain of devices.) Turn on the answering machine and set the outgoing message and number of rings as per the directions for the answering machine.
If you have any problems, make sure that the line is good. I use an old rotary phone to check my service connection (at the box since that has RJ-11 connections in my home). You may want your phone company to check if the line is good to your home if the service doesn't have RJ-11 connections. If the problem is in the wiring, check the jacks (loose wire/broken wire) and exposed wiring (missing insulation/breaks). You may need a professional to check in the walls; your telephone service provider will fix this for a fee. If the problem is outside, then the provider will fix it free.
You can get the manual and guick start guide as PDF files from AT&T: http://telephones.att.com/att/index.cfm/product-detail/?ProductID=290
. The links are on the right hand side of the page.
I hope this helps.