Those "sources with knowledge" are at it again, this time stirring the pot over a possible BlackBerry-branded music service. According to both CNET and Reuters, said sources revealed that RIM is in negotiations with "the four largest record companies" to launch a service that would "run on top of BlackBerry Messenger." What that means, exactly, is anyone's guess at the moment, but word is the mobile phone maker has already signed one label, and is close to snagging two more. Could this be the move RIM needs to shake off its enterprise-only reputation? We'll just have to wait and see -- according to Reuters, the service is expected to be announced by September 5th.