It's really strange the contortions of logic that people put themselves through to convince themselves and others that the n900 is not a phone.

Of course it's a phone. End of.

The issue really becomes one of expectations.
The 770, n800 and n810 were not phones. In many ways they worked really well and were great devices but had some bugs and limitations that were accepted by most because of what they could do very well.
If the n900 was not a phone and was just another progression up from the 770/n800/n810 then I'd expect similar i.e. it would work very well in many areas but have some limitations and would be satisfied enough if that's the way it worked out.

However my expectations of a phone would be different and I'd be a lot less tolerant of poor performance. If my phone was glitchy, unexpectedly rebooted itself or similar I'd be back to the phone shop to replace it or look for a refund.

As the n900 is marketed as a phone, is sold in phone shops, is labelled everywhere as a phone then it's a frickin' phone.
It has to match the expectations one would have of a phone regardeless of all the extra bells and whistles it includes.

And if it doesn't it should take the flak.