An ENUM address reverses a standard phone number and adds an additional code for recognition by e-mail systems. Over 100 billion potential combinations are possible with the 11 digit system.
The theory behind the proposed mass allocation of numbers is that technology can be developed by telcos to direct different forms of communication using just one number and giving individuals the means to choose the medium by which they are contacted and by whom.
Critics in the US have expressed concern that the ENUM would affect the relative anonymity that users enjoy on the internet, whilst also affecting the security of public phone systems. The US Centre for Democracy and Technology, a privacy group based in Washington, is campaigning for the right to opt-out of the scheme. The Centre and other privacy groups fear that an ENUM database would represent a major risk of privacy invasion, although it is not yet known if or how the scheme will be rolled-out.