The British Phonographic Industry is doing it now: 
http://www.besonic.com/BeSonic/News/0,4756,g0r0l0t0o0i22016,FF.html

and the RIAA did it last year:
http://www.wired.com/news/digiwood/0,1412,58676,00.html

but they refused to identify the third-party company providing the service. 

What is the company that the RIAA used to send out the 4 million IMs via Kazaa?

I'm pretty sure that BayTSP were involved: http://www.baytsp.com/.

You might also want to look at http://news.bbc.co.uk/1/hi/technology/3104281.stm.

Hope this helps,

JP

Thx JP, but I don't think BayTSP is the one that was/is doing the
Instant Messaging. If they were, you'd think they would have some
reference to it in the Press pages on their site.

As I understand, the actual company responsible was - obviously - not
keen to reveal its identity, given that their actions would lead to
widespread reprisals in the form of denial-of-service attacks and the
like. I've seen people point their fingers at BayTSP in a number of
forum posts (I was researching a related article) but, obviously, this
isn't the qualified answer you're seeking.

I've got a deadline at the moment, so don't have the time to
investigate this further, but the following list of companies might
help...

? BigChampagne
? BayTSP
? Cyveillance
? MediaDefender
? MediaSentry
? NetPD
? Overpeer
? Ranger Online
? Vidius

Good luck!

JP