Having issue with your iPhone 4S WIFI become unavailable or greyed out? Have you tried resetting it, and still not working? Or maybe cooling down your iPhone for 15 minutes but that's a temporary fix and WIFI will become unavailable again.
If you tried all above and still now working for you, try reseting your iPhone settings using factory default. Here's how to reset your iPhone using factory default.
- In your iPhone, touch the Settings icon.
- Scroll down to General.
- In General settings, scroll down and touch Reset
- And here you will see the Erase All Content and Settings. See the screen captured courtesy by oxdaily.com