i'm a customer service representative, I've been working for TMOUS for the past 4 years.
Wi Fi calling, has nothing to do with your capped data package ie 200 mb/ 2GB/ 5gb/ 10gb plans.. Wifi calling feature is using your source of cable or dsl connect via wireless router.
IF you're worried you many use all your minutes, then call 611 and ask your agent to add the free unlimited wifi calling. simple.
second part, hotspot is kinda different, its tethering using the data service and yes this can cause reduced speeds. no separate bucket, just the one i mention above... keep track of your usage by dailing #963# and hit the call key.
---------- Post added at 02:00 AM ---------- Previous post was at 01:51 AM ----------
You can use it for free as long you don't exceed your plan's limit. It counts against your data allowance, but if you continuously go over the limit, T-Mobile will send you a notice. And if you disregard it they will block the tethering on your phone. Now, if you buy a tethering plan, it will be separate from your phone's data plan.
my network will let you use it free for about 100 mb before, you receive a text message requesting you call tmous cs to add tether to your account per line using this feature at $15 per month. (you can't be with the 200mb plan) >
the network reads the mac address of your computer.. ipods and simple device seems to slip by without alert.