If you're on a call and you hear a beep, call waiting is notifying you of an incoming call. You can either answer the incoming call, or ignore it and let it go to voicemail.
To answer an incoming call:
Tell the person you're talking with you have an incoming call.
Press and release your phone's receiver, Flash, or Recall button. (The button you press and release depends on the type of phone you have.)
Your first caller will be placed on hold and you'll be connected to the incoming call. You can toggle between calls by pressing the phone's receiver, Flash, or Recall button (depending on the type of phone you have).
If you plan to take the incoming call, that is, to end the current call, just hang up. Your phone will ring, and when you answer, the incoming caller will be on the line.
Call waiting and FAX transmissions
Because call waiting can interfere with some fax machines, you can temporarily disable call waiting by dialing *57 before sending or receiving a fax. To re-enable call waiting, dial *56 after transmission is complete.