The first place I went to look was Google, of course. "s60 python api doc" first of all gives me a couple of links to the LightBlue bluetooth API project which is not what I'm looking for. The next link is to Nokia forum so that looks promising but turns out to be an old PDF file. Fifth link down I find a link to the Nokia open-source wiki at http://wiki.opensource.nokia.com/projects/PyS60_documentation.
Disapointingly the latest doc available is in PDF format which I can't read on my phone. Still, I've downloaded the PDF and I'll look for a reader.