If you update your iPhone 4S to 6.0.1 through Wi-Fi, does it erase all your data?

I have updated to 6.0 before on my laptop in iTunes, but strangely it didn't erase all my data, so I didn't have to back up. I didn't see it automatically back up during the process of updating, so I was wondering if it would erase all my iPhone data if I updated it through Wi-Fi.

A few months before, when I updated to 5.1.1 it erased all my data. I'm not sure if Apple did anything to 6.0 that made it not erase my data…

No, it doesn't erase all your data. I upgraded my iPhone 4S (v. 5.1.1.) to v.6.0.1 on Wi-Fi… It kept everything!

Entirely depends on your luck. Well really!

If the upgrade is successful… Then you get to keep everything.
If not - like it gets stuck in recovery of DFU mode, then there's a risk.

So this is what I'd recommend - foremost backup your iPhone via iTunes (in case things go bad). When you connect your iPhone to iTunes, it shows up on the right hand side. Right click and select backup.

Then upgrade over Wi-Fi or whatever other means.

If you get stuck, you can get a software like Total Saver from MyPhoneData and extract all the data from the backup of your iPhone.