Supplementary Services

Hi.

I've just sent 4 patches to ML - that's cosmetic adaptation of work by Tobias Engel (tobias/supplementary_services branch) from few years back to current master.

Not sure if I should put sign-off in the commits but I certainly don't claim to be author of the code. Anyway, I'd like to see this pushed forward cause I think it's useful functionality better suited for master branch - would be shame to let it bitrot :)

Comments and suggestions are appreciated as usual.