AFIK, none in production. Many lab environments but REAL 4G does not exist in Commercial Production yet.
LTE is not 4G.
IEEE 802.16m/WiMAX 2 is.
4G is standardized and will make things better but differences in Frequency usage across the planet will still cause some roaming issues.
Multi band phones will help but still...
There are still kinks to sort out with 4G..Antenna Tech among others...to get the bandwidth required to meet 4G specs.
Plus, there are no real 4G handsets out as yet either...the LTE handsets are just LTE handsets..not 4G.
Presently, many markets are using LTE just for data.
4G should and will also allow Voice over LTE...then that will be true 4G.
Till then, we stuck on 3.9G !