iPhone 4S tether should be present even without Jailbreaking.

If you are using Safaricom, go to Settings > General > Network > Cellular Data Network and enter the APN as safaricom and leave the username and password blank.

If you are on Airtel, use whatever APN they use nowadays/

The tethering on the iPhone tends not to work if the APN if not explicitly defines even on network that would normally work with a blank APN.