Missed call scams start by ringing your phone and hanging up so quickly that you can’t answer the call in time. Your phone registers a missed call and you probably won’t recognise the number. People will often then call the number back to find out who it is. Apart from being a nuisance, the missed call can lead to a scam in two ways:
The number you call back may be redirected to a premium rate service (a number that starts with 190) without your knowledge, which means you will be charged a lot of money per minute.
The number may tell you that you have won a prize of some sort and give you another number to call to ‘claim’ your prize, but they may not tell you how much the call will cost. This second number may be a premium rate number, again charging you a lot of money to get your ‘prize’. Your prize may be nothing more than a ring tone subscription—which can also be a scam!
Text message scams work by sending you a text message from a number you may not recognise, but the content of the message could sound like it’s from a friend—for instance ‘Hi, it’s John. I’m back! When do you want to catch up?’ or ‘Hey big fella, happy birthday!’.
Another common tactic is for a text message to sound like someone flirting with you. Many people reply asking who it is and end up engaging in a lengthy SMS exchange with the scammer. Only later do they find out that they have been charged a high rate both for messages they sent (sometimes there are also charges for messages received as well).
http://www.scamwatch.gov.au/content/index.phtml/tag/MissedCallsTextMessages