When you hear a busy tone after dialling a telephone number, simply dial 5. A recorded message will tell you if your Ring Back request has been accepted. If it has, you can hang up and your phone will keep trying that number until it's free. When it is, your phone will ring and you'll be connected. Ring Back will keep trying a busy number for up to 45 minutes.

Note: This service costs 15p per use plus the cost of the telephone call unless you subscribe to a monthly inclusive Ring Back calling feature.