I really want the iOS7 software update

I have an iPhone 4S & my service is under those cheap services for example like net 10 or simple mobile, but I heard updating the new iOS on my phone will cause damage to it? Is it true? Should I do it?

And you actually believed that an official software update will brick your phone? You must be one of those people who bought an iPhone "because it's cool."
Anyways, no. It won't cause damage to it. It's released on Sept. 18.

No, iOS 7 will not damage the iPhone.

iOS 7 is available on September 18 for the iPhone 5, 4S and 4.

http://gigaom.com/2013/09/10/ios-7-is-available-on-september-18-for-certain-devices/

It's not true that it will cause some damage. I recommend you to wait for few days to update IOS 7 because till then you will get official reviews and software to download.

After all IOS 7 will be realeasd in 18 sep 2013.

P.S: If it cause damages too you can downgrade to lower version.
Any confusion: hit me message!