Panasonic KX-TG985 Not using a land line, says "Check Tel Line" :-(

Panasonic KX-TG985 Not using a land line, says "Check Tel Line" :-(

I am not using a landline and will not be using a landline. Can I make it stop showing "Check Tel Line"? I’m using it with two cell phones, no problem there, but I don’t want it to keep showing “Check Tel Line". REWARD for USEFUL ANSWER.