Hi all,
Thought I would share my solution to a problem I was having with free international data roaming my Samsung S4. In Canada, UK, and Ireland, my phone would initially connect to international roaming without a problem but would stop working within 10 mins or so. I searched the boards and found lots of threads about changing the APN settings, making sure mobile data roaming was on, etc. but none of those did the trick.
What solved the problem for me going to Settings>>Mobile Networks and then setting the "Network Mode" to GSM only. Once I made this change the phone would stay solidly connected to the EDGE data network without a problem.
I think the problem is that if you leave the phone in one of the "auto connect" network modes it keeps trying to hook up to the 3G and/or 4G network and that causes a conflict (in the UK I would initially get a 3G connection before the connection went dead). This issue may be unique to the S4 but if you have having trouble maintaining connection to free international data roaming with any phone my advice would be to would try switching the network mode to GSM only.
Hope this helps someone,
Bill