Pretty much, but it's already happening and will be completed over the next number of months.
I won't be surprised if there are a
few hiccups in switching over. It's never easy to work on a live network. (When last did you replace the rings on your car
while the engine is running?

)
But the end result will be better coverage, latency, reliability and bigger speeds, right up to LTE.
Actually now that I think about it, the site that covers me was supposed to switch over last night.
/truddles of to do some tests.....