OK, so I know who this is now - they called again today and didn't hang up when I answered. It is the RSPCA - at least that's what they said before I replied I wasn't interested and hung up.

Several calls today,no-one on the other end

Even though you are on the Do Not Call register, Charities and Research companies are still allowed to ring you unfortunately.  They must also allow their phone number to be displayed to the person they are ringing.  I believe it is a charity ringing- I have had two dead calls from this number.  There is a machine that dials numbers and registers if it is answered, it then records the time and day.  This is so that a human can judge when to call without wasting time if someone is not normally home at that time.  A trick I learned from Neighbourhood watch is to press # as many times as you realize no one is going to answer.  This confuses the machine and it throws your number off it's list and will not ring you again.  Hope this helps someone.

How many of you are on the Do Not Call register like me?I have just phoned Telstra unwanted calls department as I have been receiving calls from this number also for several days now. The phone number is not a Telstra number so I presume it's an Optus one, plus the assistant told me the number is only for making outgoing calls not for receiving. I smell a rat and wonder how many places have been burgled that have already received calls.

I have been receiving calls also from this number. Nobody speaks if I answer and every time I have phoned the number I only get busy tone.

This number routinely calls and never leaves a message or hangs up if I answer.