Yes I think this was incredibly clever and made the 2G network seem less. Then there was the court case from Arqiva against EE which stopped the 3G integration, and once that was resolved (EE won) the 4G decision from Ofcom had occurred, so EE was permitted to roll out 4G on the existing 1800mhz - so the rebranding started fast.
I don't think they just left 1 network working and ripped out the other.
Except in Northern Ireland, correct.
My phone regularly changed between "Orange" "T-Mobile" and "Orange T-Mobile" on the display before I got upgraded to a EE sim. (that was with a Orange and T-Mobile SIM in different phones).
Will be interesting to see what happens if the 3/O2 merger is allowed because I use O2 in a company supplied phone and the coverage is diabolical out of town. 3G is almost non existent. Vodafone is worse, and as others have said they will have to lots of upgrading to keep up.
Where vodafone have rolled out 4G it is a dramatic improvement, my work is with vodafone and it was awful only 18 months ago, and now its amazingly better (3G and 4G).
O2 and three is one to watch, I think it won't be allowed to be honest.