Disclaimer: I do not (yet) have my Pinephone.

> 1) Is a Pinephone a viable alternative either iOS or Android?

A Pinephone will never support all the proprietary apps (Facebook, Instagram, Snapchat, TikTok, Fortnite, etc). In order to be viable, I would say a phone needs to support phone calls, SMS, MMS, camera, GPS/Navigation, and have a fast and snappy web browser. Currently the Pinephone supports everything except MMS (which is necessary for "texting" pictures and groups). Because you will not have access to FB Messenger, Whatsapp, Instagram, Snapchat, etc on a Pinephone, you will have to you SMS/MMS for communication if you want to interoperate with people from the mainstream.

2) For T-Mobile based carriers in the US, you just stick in the simcard.