I apologise for waking up this old thread... Charging via NFC (instead of Qi, or besides Qi) is possible. If the receiver is inclined to use the power received to charge the battery. And the power is usually not higher than 1W, as KTy noted.
Benefits of NFC-enabled wireless charging over lower operating frequencies typically used in wireless charging include lighter antennas, and lower parasitic heating of metallic stray objects.
Besides, adding Near-Field Communication to N900 would be a benefit by itself.
The question is: would adding NFC-antenna to N900, and finding an external NFC-charger, be easier than doing the same with an Energiser Qi wireless charging kit? And the notable disadvantage of NFC-charging is relatively low charging power level (between 0.1W and 1W, while Qi is supplying around 5W?).
I am rising this question because I see the ubiquitous MIFARE and other ISO/IEC 14443-based contactless smart cards, and I hope that it would be possible to charge a mobile phone, when needed, from one of the terminal readers. Clutching at straws, yes, but these terminals seem to be more compatible with each other than power grid in different countries.
Still, as NFC-charging is slow... When you have more than enough power for your needs, an interesting feature would be to communicate with other NFC-enabled devices, including, with appropriate programming, the validators within buses, trams, trains and boats, or the cards within your wallet. However, the protocols of this widespread devices are quite complicated, I expect, as they wish to secure the payment systems from possible cheating.
Still, even ePassport chips can have their data cloned and altered.
Best wishes.