The same problem with my 520, had an LCD problem but it's been fixed, it seems the 8.1 has a problem in 3G even though I'm only using the network's prepaid plan, but when I'm home Wi-Fi works perfectly, I know theyre different but when I transfer my SIM to my Nokia X and turning on the cellular data I can browse online, no problem whatsover, unlike now in my 520 it doesnt work, at 8.0 browsing is as smooth as silk, so I would like to know if there are the same issues on 8.1 regarding 3G with other Lumias? Oh, it's all been set to 3G and even 2G doesnt work, signal strength is good both 3G/Wi-Fi in Nokia X (same network provider), 520 cant browse online in 3G/2G but fine in Wi-Fi