Hi, we have a person that has a replacement phone of a different model. They originally had a 3903 headset and their replacement is a 2616. We've set it up exactly like other 2616's on the system but it has no dial tone. Tested the replacement 2616 on another line with a 2616 and it it fine, but plugging any 2616 on the line that the 3903 was on has no dial tone. Do you have any recommendation or things to try? Thanks!