Well, I have now done the tone system - named tones with defined sequences of frequencies and levels and option to combine two frequencies. We have defined the standard signalling tones for BT SIN350 (e.g. ring tone, engaged tone, etc).
We have a configuration option to allow tones to be redefined.
I have a test brick on [phone number removed] at present, which just answers with a tone.
I think enough for today - call routing logic tomorrow I think.
P.S. This is what it plays (wav file) - I'll delete the number tomorrow.