If grandma still doesn't know what call waiting is and you need to talk to her right away, follow these easy steps to interrupt calls. You'll later be charged a fee by your phone company, which likely will be somewhere between $5 and $10.
Interrupting a Call
Hang up when you get a busy signal. You can interrupt a call only by contacting the operator.
Dial "0." Tell the operator that you have an emergency or that you need to interrupt a call. Give the operator the person's number.
The operator will interrupt the other party's call and inform the person that you are trying to get through and to clear the line.
Hang up, then again call the person you are trying to reach. If the person has disconnected from the other call as requested, you'll be able to get through.