Now that I have updated to iOS 6 on my iPhone 4, I find that whenever I put the phone to sleep mode, it will disconnect from WiFi/3G. Then when I wake it, it has to reconnect again.
Therefore, I don't receive any of my WiFi notifactions (like Whatsapp messages or Viber calls) when the phone is asleep.
View the Correct Answer TS1398 iOS 6 constantly disconnects from WiFi/3G when in Sleep mode in iPhone problem Correct Answer , iPhone Wi-Fi, 3G and Bluetooth errors Answer