After updating mine Vodafone iPhone 4 to iOS 5, all was working well, except no data connection.
Error: Could not activate cellular data network. You are not subscribed to a cellular data service.
I found mine solution at: http://www.iphoneclub.nl/iphone-tips/telefoonfuncties/probleem-met-mobiele-datanetwerk-oplossen/
One very nice thing about the iOS 5 update, is the return of Personal Hotspot. On my iOS 4.3.3 update the menu item Personal Hotspot disappeared, now it’s back, so I can share mine internet connection on my iPhone with other devices.