I have changed my csc to eux and am on latest firmware for uk but still have no beta in members app available, I'm on 3 network but device allows any sim card so it's unlocked.
I've not had anything show up, and I feel like if I was still using my original account it would have done it, as I used to be able to do it before I lost my details.
Changing your csc won't make any difference so you just can get the beta 6 firmware. If you have flashed your device then you'll risked bricking your experience device in doing so.
