I think it has an voip config, i tried configuring in some app but did not worked that time. If someone good at voip config would be a great help. I did asked airtel guyes they don’t know anything about it.
I am using Panasonic kx ts500mx that was lying around for 2 decades at my Grandparents house. It doesn't have a screen. I have added speed dial from router's setting to make things a little bit easy.