I haven't tried VOIP. Skype chat works great.
GPS is still in need of serious work.
Browsing is surprisingly good--great for checking news or TV listings.
First and foremost, a cell phone. I don't have a landline, so my cell phone is both my personal and business communicator. The N900 has a great GSM radio with fewer missed and dropped calls than my previous SE Z710i. BTW, I'm on Fido on Vancouver Island. HOORAY N900!
Second and very important: ability to hold ALL my contacts, appointments, tasks and notes from Outlook. HOORAY! I have over 4000 records on the N900. I've never used other smartphones, but my previous regular cell phones absolutely SUCKED at this.
However, Nokia PC Suite is giving me some grief, so the picture isn't completely perfect yet. Also, the PDA/PIM functionality is still pretty basic, e.g. cannot edit a contact from within the Phone app. I am hopeful these little issues will be worked out over time.
Third, a music player. HOORAY! I have about 11 GBs of music and album art on the N900. The Media Player is basic but it works OK. Much better than my SE Z710i (shame on you Sony!). Only missing functionality is support for my Audible.com audio books, and I'm hopeful that will be added in due course.
Fourth, a decent camera. Again, HOORAY! The Camera app is pretty basic, but it works OK and the pix can be quite good, much better than the iPhone as I'm told. And it BLOWS AWAY my other phones.
As a bonus, the movie feature is also surprisingly good. There's an issue with the little chrome trim around the camera lens, but I expec that will be fixed (replaced with a black ring perhaps).
Fifth, a GPS. The N900 GPS receiver seems OK, but the Ovi Maps app is disappointing. First thing to do is download all the maps for your area ahead of time so you don't need a data connection to at least see where you are. I downloaded all of North America. However, Ovi Maps still demands a data connection to find addresses and do routing, which is rude. The "Track Me" only works with a route, etc. I eagerly await an upgrade, otherwise GPS is pretty much useless to me on the N900.
Sixth, a decent calculator. Since I've been an HP RPN fanboy since the HP-35 and HP-41, I installed Free42 right away. YES! You won't believe how LAME the calculator is on the SE Z710i.
Things I wasn't looking for, but which work surprisingly well: - Web browser with Flash, nice! I'm not into a cell data plan, but when there's WiFi, it's nice to grab the news or check ferry schedules.
- Streaming media from all my Windows 7 media servers, VERY nice! I gather the iPhone can't do that? So I don't need to lug my laptop around the house to watch Photoshop User TV!
Integrated IM. All my MSN, Yahoo and Skype contacts now appear on the phone in one App.
- Sketch app. With a stylus and the awesome screen, there is actually some potential to use the N900 for on-the-spot llustration and artwork. This wouldn't be possible on a capacitive screen
I'm looking forward to trying the KOffice drawing apps whether they're released.