Mobile phone tours in museums have enough mainstream awareness to merit an article in The Age, but as the article points out, there are issues with roaming and mobile call costs. There’s no mention of implementation at any Australian museums, but I don’t know if that’s because there aren’t any, or because the article was bought from overseas.
I think podcasts are also a viable alternative. I’d love to see links between city tourism and museums so that people can hear museum content over a whole city.