I am using Lumia 620 since 3-4 months but facing a network related issue. When my cell is on standby like for 4-5 hours(when I am asleep). it leaves network but shows full strength what I meant that after these 4-5 hours if anybody tries to call me it says the number is switched off but everything works even if I am using Internet Explorer on WIFI unless I do some outgoing network activity... Only after this outgoing activity I am able to receive call.? anybody had this issue?