No dial tone, just buzzing noise - should be 2 line phone, 1 jack

Just bought Uniden Tru9466 cordless, 2 line operation phone. After charging, everything seems to work fine except the 2 line operation itself. When plugged into the jack w/ two lines, all i get is a buzzing noise. When plugged into my fax line or dsl line jacks (which are just a single line) I get a dial tone and can use the phone as normal. I have tried plugging it in at a different jack with no luck.