In reply to Nadir khan:
There's some information on winter climbing here:
http://www.edinburghjmcs.org.uk/pdfs/iceland.pdf
There's also long glacier climbs on the SE side of Vatnajökull and endless amounts to do in the Interior. Most places can feel off the beaten track in winter, even 5 minutes off the Ring Road.
On our trip across the interior this summer we were told that taking a satellite phone would not be excessive. In the end we took Personal Locator Beacons, and if you are heading anywhere remote (esp in winter) without backup, they're definitely worth considering. A friend who is extremely experienced in Iceland was immobilised when he put his back out whilst pitching his tent when attempting a solo winter traverse of an icecap. Fortunately he had a PLB, but he reckoned the 12 hours he waited for rescue were the scariest of his life!
It's worth keeping a bit of an eye on the traffic webcams: they will give you a pretty good idea of how fickle conditions can be in the south in winter.
http://www.vegagerdin.is/english/web-cams/
I've not been north in winter, but access would be a fair bit more tricky than the south, but it's much more likely to provide decent conditions.
http://www.vegagerdin.is/english/road-conditions-and-weather/the-entire-cou...
We have found this Norwegian website more reliable for weather in the interior (if you can get a signal) than the Icelandic Met Office - though the latter has a nice seismicity page which could be useful!
http://www.yr.no/place/Iceland/
http://en.vedur.is/
HTH