Cordless phone says "No line", no dial tone and answering machine doesn't work
Problem was that the cordless phone said "No line" and there was no dial tone. Switched handset in base and "No line" went away, but still no dial tone, couldn't play messages, ans. mach. did not pick up, no one could hear if they called me. Power worked because lights were on phone. Our corded phone worked fine and worked when plugged into cordless phone jack and with cordless phone's phone cord. Solution (from AT&T Customer TechSupport):
"Unplug the power source on base phone, then unplug each battery on each handset. Wait a minute then re-plug base and other phones. Your messages remain. Your directory remains. You must reset the date."
Of note: My model was EL52303 which was NOT recognized on the AT&T online form, and message would not send. AT&T line busy and no one called back. Tried again and got awesome agent who gave me advice above.