Please clarify... do you mean that a call is ringing in on the second key, but same extension number, that you are currently talking on? If that is the case, then you have selected to be able to receive more than one call at a time (on that extension), which expects that you will put the first call on hold, and take the second call, or, wait until the time-out period for the second call to go off to voicemail on its' own. If you want a second call to go directly to VM when engaged, then disable the option to accept a second call.