Thanks for your comments Warin61 and for your links to the mailing list TheSwavu. I feel a bit silly now about this diary now I’ve read through the WikiProject page for Australia.

Never seen the phone:*= used … don’t know if it is implemented. I would tend to keep the phone=1800 etc as it is, no country code.

This was silly of me, given the phone:*= tag isn’t an official tag. Luckily I hadn’t encountered too many edits where I did this, so reverting my changes should be easy.

I don’t know the copyright situation on any published phone code boundaries, go carefully there.

I’m going to be much more careful about this. The data catalogue page on the wiki that I found has been really useful in this regard.

I don’t know who set up the MapRoulette challenge but this has been discussed on the talk-au mail list

I had not thought about checking the mailing list, so thanks for the links. Thankfully it seems these answers are now on the tagging guidelines page on the wiki.