The next part of the question is, even if I have a LatLon.. how can I display it on a Map which is in an application that requires Dues.
Again with Google wanting $10,000.
I cannot speak to the first part, but as for the timezoneId yes, it is in the same form as the Olson Timezone Database.
Just recently this service stopped working for my application, returning a 'Urgent: please contact: info@geonames.org' status. There may be something we have to clear with GeoNames before committing this to a release.