Is Virgin Mobile UK GSM or CDMA and Can I Buy an iPhone 5s with it Unlocked UK?

I Know te New iPhone 5s is coming out and I wan to get it unlocked in UK but I have a Virgin Mobile sim and People Said that I can't use Virgin Mobil because its CDMA and iPhone 5s Unlocked from Apple store is Only for GSM so I Want to know if Its GSM or CDMA an if I can Buy an iPhone 5s with it or not?

Virgin mobile also has GSM sims. So they can be used on iphone without any problems