It could be the head set.
You can verify it by logging into the system, going to maintenance commands and enter "loc feat ex <extn>"
It will show you if the headset feature is turned on.
Then the easiest thing I've found to tell customers how to fix, (aside from using a feature code) is to program a headset button on the phone by pressing the blue key and then a vacant key on the phone and scrolling through the menu until you find the headset button and save it.
Or else, log into the 3300, go to all forms, then feature access codes and find out what the real code is for the headset. I suspect you're not using the right one.
Ralph
Baby Nursery Supplies