Default wifi calling and tethering question

Hi folks,

I just got this phone yesterday (LG G2) and I enjoy the wifi calling since i don't get any service in my area. I want to root my phone so i can throw some roms on there but I have two questions:

1. when I put on a custom rom, will wifi calling still work?
2. I have unlimited 4g LTE. the T-Mobile sales rep say that I have 2.5gb dedicated to tethering. Will the custom rom ignore that 2.5gb limit?