How can I get more details about information in a NOTAM?
What, you dislike the fact that the NOTAM about patchy ice is patchy in its detail? :)

Generally if you need more information about a NOTAM (in the US) you can check with:


Flight Service
While collecting your briefing ask if they have any more detail -- sometimes they do, sometimes they don't, but it's worth asking.  
A local FBO
Particularly for FICON NOTAMs - A local FBO will usually know the condition of the field, and often have other useful info for you (like how much a heated hangar is going to cost you for the night).
Airport Operations
Again, particularly for FICON NOTAMs - These guys will usually have a pretty good picture of the field's condition, since they're generally the poor shmucks responsible for doing the snow/ice clearing.  


Failing all of those, you can also call the tower phone number at a towered field (you can get that number from Flight Service too) and ask them for details.
I usually make the tower my last resort call - they're almost certainly going to be willing to give you as much information as they can, but they're also busy doing other stuff like dealing with planes taking off/landing/taxiing around &amp; they'd probably appreciate if we tried the other sources first.
The other folks I mentioned generally have someone sitting around to answer phones and questions.
In the case of Flight Service, that's basically their job :-)