I have owned my SII for approx 18 months now and in the past two months my phone sometimes goes into like a "frozen" mode. No error messages are reflected and everything on the screen appears normal. Signal strength shows full (or almost full) number of bars. I only realise something is wrong when people start telling me that they cannot get hold of me or that they immediately get my voice message when they try to phone me. I also realise that my messages are not being delivered. If I then reboot mt phone all the missed calls notifications, messages and whatever suddenly come through. This is highly frustrating as I never know in what "state" my phone is in. Can anyone help? I would be very grateful.