I'm an existing 3 customer (since about June this year), and I noticed my phone using the Orange network for the first time on Tuesday (19th Dec). At first it was showing 'Orange UK' on the screen whenever it roamed onto Orange, but it looks like 3 must have sent out an update to my phone, as Orange is now listed as '3' when I do a network search, just like O2 was (and still is).