Not able to see 'iPhone Cellular calls' on iPhone 4s

Hi There,

I have iPhone 4s (running OS 9.1) and MacbookPro (running OS Yosemite 10.10.5). Im trying to make calls from my Mac , but while doing that it throws me error that your devices should be on same network. Im guaranteed that they are in same network.

But after digging for some time , I found that 'iPhone Cellular Calls' option is not available on my iPhone. Any specific reason for that ?

I have logged in with my AppleID on both the devices. Can anyone help ?