I thinked about this deeply last night and I found one point.

Both iphone and Android phone can upgrade their OS.

But N900 cannot. Also, all NOKIA phones cannot upgrade OS.

It's just like on my PC, I can use Ubuntu 8.04.3.
I can also install 8.10 or 9.04 or 9.10.
When 10.04 release on Apr.2010, of course, I can install it on my PC.

But it seems that NOKIA's "rule" is to make the mobile phone and OS a bundle. For instance, you cannot install Maemo 5 on N810.
and it seems Maemo 6 cannot run properly on N900.

I think this "NOKIA rule" may be OK with some S40 low-end (entry level) mobile phones. But for smart phone market, it should not be taken.

So I am wondering whether NOKIA could provide a CD image
or some thing like that to let the end user install the OS by ourselves,
just like what Apple does.