Originally Posted by
Sant
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.
Vodafone subs in Europe and Asia seem to accept voice and SMS services and are now blocking data for TMO - there are ALWAYS other carriers to choose in such countries.
On an iPhone ensure you have a 3G or LTE (select networks only) showing to ensure data is active
On various Android phones it differs; best to do a *#*#4636#*#* in the dialer and select phone info or device info and see that GPRS says "Connected" - will also list type of service under Network Type:
If it doesn't show data then ensure "Data Roaming is on" ensure, on the phone, on the account, dial #RON#
If it still doesn't work pick another network
To help others if you find a network working for data that is not in the Wiki please edit the wiki or highlight it working here. Same on networks that let you connect for voice and SMS only BUT NOT data ; we want to list those under problem networks.
Back to OP: There was a concept of preferred networks on a SIM card eons ago. NO carrier seems to use this now; this allowed the home carrier to do a SIM update populating network number ID's of preferred roaming networks so those got picked over other networks first. No US carriers seem to be doing this and it looks like most smartphone radio software isn't reading this anyway... SHAME!