I spent ages on the phone / web chat / in store with O2 tech support yesterday. They were all friendly enough, but what a shambles the tech team are. Ended up being fobbed off from one team to another repeatedly.
O2 are aware of a general problem with S4's, even some of the devices supplied directly by O2 themselves (like mine). See http://www.o2.co.uk/samsung-software for details.
Apparently, you need baseband version 19505XXUDMH8 or 19505XXUBMF8 to use 4G. If your S4 device has the O2 logo, then you will be able to download one of these versions using Samsung Kies.
If, like me, your baseband version is I9505XXUBMGA, and you have no O2 logo on your screen then you're out of luck. Even if the phone was supplied by O2 themselves. You're stuck on 3G and you'll need to wait for either O2 or Samsung to get their act together and make the software update available to your device.
To check your version: From the home screen, menu, settings, more, about device.
It looks like this information hasn't yet been made available to O2's tech support staff. If you call them, be prepared for a long and frustrating waste of time for both you and them.
I'd hate to be working on the O2 tech support team right now. Nothing like having a call queue full of frustrated customers and your employer not sharing all the facts with you.
