I'm not sure if there were any more or less open handsets, but i bet there are some, just not that popular, or maybe projects died, and i want to thank Nokia to looking forward for open source.
But ...
There are a lot of companies contributing to open source, and i mean adding patches and source to kernel and so on, and even some of them don't get profit of it. While Nokia just bought QT, and as i see the contribution in QT and opening source of Symbian kinda helping Nokia as well, to make people and communities as ours to contribute in projects.
And going open source is not only when you distribution with open code and you can get root. Open source is also life style, especially when you have community, and on one hand Nokia workers are communicating with us (e.g. is you), but still we don't even have the maemo roadmap of development, we don't know what's going on, and i don't think that there are any decisions (which we also don't know) are based on our opinions at all. (i'm not demanding to do what we want, but to consider the end-user opinions is important). Also as Maemo open source, it's still comming to us as a big peace instead of parts and there are more and more.
My point is that to be open is not only to show us code.

And i'm not saying it as negative thing, I just say that it's not excuse "we are most open", and still there are a lot of thing Nokia has to learn.