I also facing that problem.. not sure whether its whatsapp problem or 3G problem (maxis)

or firmware problem.. but earlier when i updated to 4.3.3 it was fine. Not until this weekend. :S

no... not fixed yet...

i actually test "push notification" with several network:
1) WIFI: ok np
2) 2G network (gprs or edge): ok np (!!!!!!)
3) 3G: die...

(notes: b4 u ask ur friend send u watsapp msg for testing, pls quit the watsapp from multitask bar (by double click home button). watsapp will online "a while" even u back to home from watsapp)

i also found i can't using 3G network download/update app.
i do reported this to maxis, so everyone pls call 123 report and make them do something. thanks.