I'm in Europe, and from simple direct testing (GT-I9505 vs SGH-I337), both in the same place (away from a big city and inside a moving train), running the same carrier, I found that the GT-I9505 had absolutely no problem running HSDPA+ speeds, whereas my SGH-I337 got up to EDGE... if I was lucky.
Inside a city there's no problem seeing that lovely H+ logo on my status bar, but anywhere else I went - nothing above EDGE.
Digging further, I learned that most of Europe (including my carrier) uses the UMTS at 900 mHz frequency for H+ data speeds, and digging more, I found that the aforementioned SGH-I337 doesn't include that particular frequency at all.
The international S4 has that frequency, even T-Mobile's version has that frequency, but not the particularly nastily locked SGH-I337 (let's not mention that damned locked bootloader).
Does my phone even have the hardware capabilities to turn on that particular UMTS frequency, and if yes, how do I unlock it?
http://forum.xda-developers.com/show....php?t=2291589 - this method unlocks AWS (I enabled AWS, haven't tested it yet).
Edit (even before posting):
http://forum.xda-developers.com/show...37&postcount=5 - following this post, I dialed *#2263# and that menu opened. In the WCDMA section there's WCDMA 900 - will it work for my specific situation?
I guess the mods will delete this thread, but have to ask, anyway.