I come across this article some weeks ago, bookmarked it, and tonight got around to reading.
If I understand this right, then this would be illegal outside the realm of internal phone to internal phone.
Playing music down the line in this way (acting like it is ring tone), would cause people to be paying for the call straight away. If effect, the ring tune would be acting like the informational/signalling tones, which are illegal to charge for.
Would this clear the legal side of it, because we can reasonably expect callers to understand that their call has actually been answered, because they are not hearing normal ring tone? Though, I don’t think a great deal of phone users could be expected to understand this, nor would I agree this would be fair to callers anyway.