My sim has 4Ggg4 printed on it if that helps?
not sure if it helps. GG bosses were saying you need a new sim when 4G is rolled out. About this time the new sims started saying 4Ggg on them, but my argument was that the sim shouldn't affect the radio, only some details that allow the phone to log onto the system using that radio.
However, I was reading today that SIMs contain some kind of authorisation encryption stuff, so maybe that needs updating for the O2 4G.
Three SIMs don't need updating though.
Anyway, I think my point is maybe these 4Ggg SIMs only allow a switch between 4G and 3G, but the 3Ggg SIMs allow 3G to 2G.
Just a thought, no evidence at all but keep it in mind.