Default [Q] Using S5 (NE9 w/ root) overseas

According to some internet research, the UK uses GSM 900/1800 w/ 3g 2100.
According to Verizon's website, their G5 has EDGE/GSM (850/900/1800/1900), HSPA/UMTS(850/900/1900/2100).

On the phone, VZW claims the phone does not work over there, but I suspect it has to do with software more than the antenna, but was not sure. Does anyone have a guide as to what is required to use a prepaid SIM for 3G when traveling in Europe?
  • HTC Rezound (rooted 4.0.3, TWRP recovery)
  • Samsung Galaxy S5 (Towelroot)
  • Asus Transformer (stock B70), with B90 dock