You can use the Call Forwarding feature on your AT&T home phone, and forward incoming calls to your AT&T cell number. Here is what you need to do:
Dial *72 or #72 and listen for the dial tone.
Next, enter your cell number to which you want to forward incoming calls
Wait to hear the confirmation tone. When that is done, the system will call your AT&T cell phone number. Once you answer that call, the feature will be activated.