I have faced a lots of problems on my lumia 520, the phone can't auto detect 3g network whereas 3g networks availabale, if you have to use 3g network then you have to manually change, second thing is that phone slide up problem, sometimes when incoming call on my phone the phones slide can't be up, and then you have to press the power button and then you will be able to receive the call. but i have already upgrade the os from windows 8 to 8.1 cyan.but didn't show any fixes yet this.......so, please kindly help me to fixed these issues......i am very frustrated about it.