Apparently it's not that easy on a windows phone, but there is a way.
Here is how you can do it,
Make a backup of your current main whatsapp, just in case something
goes wrong. (This version will remain in your phone memory)
Download the mod Whatsapp WPH. Download link can be found in this article.
Connect phone to pc and deploy mod Whatsapp WPH using ...
OK, I have the answer, but sorry, Kolappan Nathan, it is not yours, as I already had the option "For limited Wi-Fi connectivity" set to "don't use mobile data." As it turns out, the phone was behaving correctly; I was misinterpreting the display.
The H symbol I was seeing, even when the data connection was disabled, was just after the network name on line 2 ...
I took long time for me to find out how I can see to which sim somebody calling.
Call is displaying in different color.
For example if call to sim 1, I see the following:
and for sim 2:
I cropped images, to show only scrennshot buttom.
Currently that feature is not available for Cortana, since currently Microsoft doesn't program Cortana to be able to make calls from a specific SIM card, but this is really a good feature to have since there are quite a large number of Windows Phones that have the dual SIM capability.
I recommend that you give this suggestion via Windows Feedback app in ...