Michael, in my instance this is directly related to Apple, there is a bug somewhere within the software that does not allow the switch even with the latest carrier settings installed. I know this for a fact as I have stated before, my friend & I are on the same carrier, we have the same software build of iOS 8.1 installed, we have the same version of carrier settings installed, he has the new settings and I dont. The only difference is he has an iPhone 5 and I have an iPhone 5S.
I believe Jaspor has hit upon something that Apple may have overlooked, that is why his information, along with all of the diagnostics & screenshots Apple have asked of me, have been forwarded to the engineering team so they can work on a fix. for those affected in the U.S. it is almost certainly a carrier issue, things work very differently over here in the UK & Europe in terms of what carriers are allowed to restrict legally, but let's not get into that, I'm getting pretty sick of having to repeat myself til I'm blue in the face to get people to actually listen to what I'm saying.
Lets agree on this, if you believe your issue is carrier related, you'll approach your carrier for support, after all it's them you need a fix from, not Apple. I have already done this, it was the first thing I did. My carrier have assured me that this is not down to them, the case I pointed out above regarding my friend having different settings to mself proves this absolutely. I will therefore wait for a fix from Apple and keep you guys informed of my progress with them, how does that sound?