Some phones don't allow for GPS to be used unless also enabling the reception for mobile calls. In other words, consider the possibility of nasty roaming charges so you plan to avoid them before you get hit by them.

I use the iOS Navigon Europe apps in pedestrian mode too. It worked well for me even on unpaved trails in park grounds in various parts of Europe. Buying the app when it's on sale using a gift card bought on sale too can really drive down the cost.