Recently upgraded my iPhone OS to iOS5. Took quite a bit of time.
A few changes on the design of the interface. The messaging is definitely much better, in the sense that now it doesn't slam the entire message right across the screen and pause what I am doing. The messages and texts are now placed somewhat less conspicuously at the top and stack up as more come in.
Another great feature is the camera and the music activation at LOCK screen when you DOUBLE-CLICK the home button. There is a pictorial explanation here if you do not know what I am talking about:
I find the Newsstand quite useless though and you can't really get it out of the way by grouping or deleting the icon.
iMessage works like a Whatsapp now. I would still use Whatsapp for international anyway.
I do realize though my contacts were supposedly wiped. And Viber doesnt work either.
1) I edited one of the entries in the Contacts, save it - all the contacts came back. Then I changed back that edit I made in the first place. This website here gives you FIVE ways to recover your contacts:
2) I reinstalled Viber. It works again. But I realize if the person you are calling doesn't have an updated version of Viber, you can't call him either.