When I was in Barcelona last month, my phone automatically selected Vodafone ES. Unfortunately, I kept getting an authentication error when accessing anything (e.g., Google Maps, iMessage). When it automatically selected a different provider later in the day and I got data service, I realized the issue could be with Vodafone.

After calling T-Mobile in the US (which fortunately was free), I was told to manually select a different service. Once I manually switched to Movistar, I got great service during the rest of my stay. Too bad the smartphone wasn't smart enough to automatically choose a more compatible service.