Sadly one you update to the latest iOS version, there is not way to downgrade or restore to an earlier version without using intricate hacks.
Restore the system to a previous restore point. Re-instasll the operating system. Send it to a computer expert for help.
system restore
Yes, when you perform a system restore it can bring back a previous virus, if that virus was saved in the system restore point.
Operating system CD
No, iPhone uses iOS as its operating system.
It allows you to restore your computer to a previous state incase of a system problem.
System Restore.
You have not indicated WHAT you want to "Restore": operating system? router?
System Restore
Restore your system using system restore to a previous date when your system worked perfectly or restore registry settings.
No. They are different. iPhone is a type of phone, whereas Androd is a type of operating system used in some phones, though not iPhones, which have their own operating system.
The Operating System found on the iPhone is called iOS which stands for i Operating Systems. The latest version is iOS 5.0.1