Yes the P990 has it's problems but my opinion is very different to the above.
1. Occasionally take pictures (feature considered desirable).
The camera produces respectable results in most daylight conditions. The flash/light isn't great though and pictures suffer in the dark.
2. Listen to music frequently (using headphones).
Reproduction through headphones is pretty good. The player is straight forward and may miss a few bangs and whistles but it does the job. Only real annoyance is that it doesn't support .ogg files.
3. Have long conversations (sometimes stretching to 3 hours).
This may be a stumbling block as depending on your set up and usage the battery life can be quite poor however mine tends to sit in it's cradle for good periods slowly charging away so I don't tend to have any problems.
4. Occasionally browse the web (feature considered desirable).
The web browser is very capable. There's no Flash though and, depending on the sites visited, there are occaisonal out of memory problems.
5. Again occasinally read/edit docs.
This all depends on the type of documents. Most straightforward M$ Office documents render well but you do loose some formatting when editing. PDF files are a bit hit and miss, some work well others not. If your looking to heavily edit documents then this isn't the machine for you. The keyboard is good for short notes, emails, etc and while creating pages of documents is possible it is not really practical.
6. Messaging - not too frequently.
SMS and emails (if short) run happily. The only problems I've had is that bluetoothed files are handled by the messaging app and receiving large files seems to cause messaging to hang sometimes. If IM is your thing I believe there are apps out there but I've never used them.
I have also read a lot about the poor performance of the p990i. But read somewhere that the new upgrade has made performance better. Can some throw some light?
I'm on a contract phone so I'm behind on the very latest versions but the updates that are available have dramatically changed the reliability and usefulness. For me it does what I need it to do and it does it well so even if there are no updates beyond the end of the year I will quite happily stick with my P990i for the next couple of years regardless of what comes along.
Hope this helps
Adam