Thanks for the question. I understand that your Wi-Fi option on an iPhone 4S is greyed out. The following article explains this issue and potential resolution:
Follow these steps to resolve the issue:
1. Verify that airplane mode is off by tapping Settings > Airplane Mode.
2. Reset the network settings by tapping Settings > General > Reset > Reset Network Settings.
Note: This will reset all network settings, including Bluetooth pairing records, Wi-Fi passwords, VPN, and APN settings
3. Ensure that your device is using the latest software. To do so, connect your device to your computer and check for updates in iTunes.
4. If your issue is still unresolved, perform a software restore in iTunes.
If you are still unable to turn Wi-Fi on, please contact Apple for support and service options.
How do I get my wifi to turn on? It remains greyed out. I have tried Network reset. Can anybody help please?
Use this article: support.apple.com/kb/ts1559
Follow all of the troubleshooting steps. You can even try restoring the device as new: support.apple.com/kb/ht4137
If the wi-fi remains greyed out, your device needs service.
If within warranty, it should be free.
If not, it will probably cost $199 USD + tax.