There is a rather interesting article at
http://www.theregister.co.uk/2004/07...kers_gut_voip/ which raises various security issues about telephone systems.
It appears that using 141 to withhold your telephone number does not in fact withhold it from everyone you call. Some large organisations can still know your withheld number and VOIP users can still get it. I once watched Bid-up.tv and on there they claimed that they knew what number you were calling from even if you withheld it. I didn't believe it at the time but reading that article suggests that they were telling the truth.
The article mentions the fact that you can spoof the telephone number that you are calling from. It makes me wonder what would happen if you received a short call from a number that had been spoofed and used ringback to call the number back. Would you be connected to the original caller or to the spoofed number?
Being able to hack into the identification data being sent on the telephone system makes me wonder if it is possible to make calls and have them charged to a number other than your own.
Any telephony experts out there who can allay fears about fraudulent usage of the telephone system?