Do I need backup for updating my phone from ios 5.1 to 5.1.1?
In short, will it cause loss of data?
You will need backup when updating your iPhone from iOS 5.1 to 5.1.1. This is because when updating there is a chance that the information on your iPhone might be wiped out. Check out http://support.apple.com/kb/HT4623 for instructions on updating.