Will Gear S Require Separate Calling Plan?

How are family plans tied together? I think similarly, the gear S2/3G can be tied into single billing. A separate service plan would not encourage anyone to buy this gear.

I want the gear add on device perhaps like 5 bucks per month to my existing plan because my total minutes usage would be the same.

I can't understand why it can't be done. Technically it should be feasible
 
How are family plans tied together? I think similarly, the gear S2/3G can be tied into single billing. A separate service plan would not encourage anyone to buy this gear.

I want the gear add on device perhaps like 5 bucks per month to my existing plan because my total minutes usage would be the same.

I can't understand why it can't be done. Technically it should be feasible

I am with Tmobile, and the adding the Gear S, was only $5 more a month, has it own number, 500mb data, unlimited calls and text.
 
It is a separate number, which means another/new phone number, new monthly fee also. But you can always set your cell to forward it's calls to the Gear S3.