iCarTel gets data about the underlying road network from a project called OpenStreetMap (openstreetmap.org). OpenStreetMap is a community-build road map that integrates data from invididual users as well as government-supplied maps, but in many cases it is less accurate than commercially sourced maps used by on-line mapping services or in-car GPS devices. When you discover an error, you can give back to OpenStreetMap by going to their website and correct the map yourself. iCarTel periodically re-imports the OpenStreetMap data, so your routes will improve over time.
Sometimes, iCarTel can't find a road segment near your current location and will refuse to route. We are working to improve iCarTel's routing algorithms; when you encounter such an error, it would be helpful if you could send us the approximate start and end locations. Also, iCarTel currently doesn't support routes of greater than 40 miles to limit the computational work that our servers have to do.
No, at this time we only have maps for the US loaded into our servers.