Yes, the 2019 Netball Live Pass will be free for Telstra customers and yes live streaming of matches, replays and highlights will be 'data-free' for Telstra Mobile customers on eligible plans.
The Netball Season kicks off with the Quad Series starting this month on Jan 14. The Suncorp Series starts on April 27.
With regards to using/tethering your tablet to your phone, If you are a Telstra Mobile customer who has taken up the offer of a free Netball Live Season Pass you can link up to 5 supported mobile devices to your Season Pass so tethering may not be necessary to use your Season Pass on your tablet.
If you have further questions , please let me know