They also don't have a way to access systems that can cost money - International calling, premium rate calling etc.

I'm guessing they are allowing access to their core network they would want to avoid any chance of unauthorised costs being incurred.

Different security levels for different risks.

I really hope Nottingham gets some 800MHz and VoLTE soon, my office at work gets either 1 bar of 4G or drops down to E, voice calls are very unreliable in here too.

This is despite getting 60Mb/s speeds if I'm outside, it's a fairly new build building so I'm guessing it's playing havoc with the signal, since I know there are a few large mobile masts close to where i work.

I'm hoping 800MHz would make some sort of difference.

3 only lets me use 1800MHz but my phone picks up a stronger 800MHz signal
Does something need activated on my end?