First I must admit to having no personal experience using VoIP through mobile phones. Some/many networks also ban VoIP data connections or sell separate (Skype?) usage packages.

But supposing service providers' policies, coverage and latency were no issues, the usability of the next Maemo device as the only telephony (and videocall?) device would also depend on its design and ergonomics. Too large or too thick is out. Pressing a bright (unless it autosenses usage) LCD screen against your oily face (when wireless headsets are inconvenient or unavailable)?

I'm not sure if Krisse is looking for positive or negative reinforcement to this idea, but certainly with the right accessories it could be done.

What is Maemo hardware wrt. VoIP? An UI with data processing capabilities and radio.

What is VoIP mostly used for today? To circumvent expensive per minute long-distance or overseas phonecalls, for videocalls (not cheap using 3G) or perhaps for privacy (with encryption) or for lines that are mostly open (such as between offices). Can (the majority of) my local contacts call my VoIP number using their local call plans?

Stationary VoIP users probably outnumber mobile phone VoIP users by a healthy margin. Personally I'd also think the VoIP ecosystem would be better if it was done via standard protocols (SIP?) instead of a single corporation (like eBay's Skype).

Localized 3G data plans can also be murderous for those who frequently travel abroad.

If a somewhat N8x0-sized tablet was my only mobile voice device, regardless of ergonomics I'd rather keep it mostly in my pocket, bag or belt pouch and would hope to see new innovative accessories to take care of the interfacing issues of making and receiving phonecalls. Watches with simple UI for handling calls and status info, dongles, clips, credit card sized remotes and what have you; and once you go down that route, why not have a tiny and dumb GSM/CDMA dongle for feeding cheap non-VoIP local calls through that system as well since the UI is already handled via (mainly) the Maemo device and/or easy call handling via its accessories. (will the next Bluetooth replacement have lower latency besides higher bandwidth?)

With mobile converged SMS & email increasingly popular I could imagine a well-designed Maemo device w/ slideout keyboard or excellent virtual keyboard being able to fulfill many needs and user cases. However providing good-enough VoIP experience depends also on the (local) data network and SIP (or Skype-like) providers.

But what if I can I hook up a very compact $200 ARM-based netbook with an (inexpensive) handset? Price will also play a role in the mix of voice and portable computing devices. What benefits would a Maemo tablet + compact netbook combo provide? A small tablet would be ideal for handwriting text entry in the many non-alphabet-based languages but now I must stop my blatant digressions before I am banned from here for good!