On iPhone 3G(S) with OffMaps you can pre-load the maps for Cuba (Havana is well covered with all the details, smaller cities less so, plenty of roads around the country). I didn't need it much but it was a great backup in the pocket.
GSM works pretty well in Cuba (mobile phones seem to be very popular with the locals) but I'm not sure how the roaming is with US carriers. From Europe it worked just like visiting any other country.
If you look like a TV crew arriving to the country, the customs may be interested in what you have but otherwise I've never encountered any interest. Last time we flew direct from/to Europe but the previous two trips have been part of RTW traveling and I had quite a bit of electronics with me, DSLR & lenses, couple of P&S's, three portable hard drives, laptop, a FullHD video camera, GPS logger, ...
They do have x-ray after the immigration so in theory they could find whatever you have. It's usually quite a mess and I think they're more into food and other biological things.