I think you mean explicitly open the port on your router, but even then that’s not true. Plex by default will proxy your traffic so that even closed off servers can be reached. It is pretty easy to disable remote access in the server settings though.
Boost or US Mobile are the new Mint. Think Boost actually has a chance of hanging around for a while since they are owned by Dish who is building out their own network of towers (think they just hit coverage of 70% of US). They also use both T-Mobile and AT&T for roaming with their rainbow sims, which is extremely rare. US Mobile is a Verizon MVNO… their “unlimited” package has the same priority as post-paid Verizon customers for the first 30gb each month, but I’m afraid they’re eventually going to get bought out by Verizon ala Mint.