Unfortunately no, you have not stumbled onto LTE.
You will start to see EE as the carrier when you used to see Orange or T- Mobile as they migrate the network.
Is that a new SIM or the older SIM you are using?
I have been running Gold Master and betas on my 4S and iPad... And not seen EE so far.... But I know it is coming.... In fact I got a text today telling me it is coming.
Here is the Tweet from EE....
"@EE: iPhone users might notice their phone now says EE. Don't worry, you're still an Orange or T-Mobile customer, only the name shown has changed"
https://twitter.com/ee/status/248491960766173184
Go to Settings > General > About and you should get a prompt that their is a carrier profile update and it will then change to EE. I was on iOS6 GM and that worked for me.
Installing iOS6 must trigger it to check for a carrier profile update.