I tried to activate personal hotspot on my iphone 4s, but i was asked to call customer care to activate this service?
Is it not a free service? do we have to activate this service?
This is a function on a iPhone rather than a service. Although Apple gives carriers options to charge users for this function as an additional service (eg. AT&T, Verizon etc..) you may use it free with StarHub, SingTel & M1. If the function is missing on your device, try following these steps.
Settings > General > Reset > Reset Network Settings > Type your Passcode if any > Reset Network Settings
This should fix any network related problems that should occur to your iPhone.
*Note: All your Wi-Fi connection settings in your iPhone will be reset. I am not liable for any damages/problems that may occur. You at your own risk.