As Virgin updated yet to 4G or is it still using EE's 3G network?
Nope.... Quite a few threads on here. Have a look at this one - goes back over 3 years http://community.virginmedia.com/t5/Virgin-Mobile/Virgin-Mobile-and-4G/td-p/1624026
Whatever customer services tell you there is unlikely to be anything soon
(They were saying soon 2 years ago)