This was published in June already, but sounds interesting:

"12 June 2008
NewScientist.com news service
David Robson

Plans to compress internet (VoIP) phone calls so they use less bandwidth could 
make them vulnerable to eavesdropping.
Most networks are currently safe, but many service providers are due to 
implement the flawed compression technology.

The new compression technique, called variable bitrate compression produces 
different size packets of data for different sounds.

That happens because the sampling rate is kept high for long complex sounds 
like "ow", but cut down for simple consonants like "c".
This variable method saves on bandwidth, while maintaining sound quality.

VoIP streams are encrypted to prevent eavesdropping.
However, a team from Johns Hopkins University in Baltimore, Maryland, US, has 
shown that simply measuring the size of packets without decoding them can 
identify whole words and phrases with a high rate of accuracy."
--clip--

More at
http://technology.newscientist.com/channel/tech/dn14124-compressed-web-phone-calls-are-easy-to-bug.html
 
Juha-Matti
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