I checked into a T-mobile store yesterday to see how this worked and what it would cost me in the end to switch over from my current plan for my 4 lines. Just to get data and sms´s onto 2/4 lines.

I was also considering adding a second line for myself, for a total of 5 lines.

T-mobile wanted a "plan migration fee" of $150 per existing line for changing over to that above plan, so I politely said hell no.

If they don´t want an extra $40/month from me than that´s fine by me.