I can speak on two things:
iPhones have limited NFC capabilities due to Apple’s lockdown of iOS. You can look here to see what the limitations are. Basic things like weblinks, phone numbers, and emails can be read, but virtual business cards are not supported.
The NExT implant has two “sides” of it. The Low Frequency side and the High Frequency (what most people refer to as NFC) side. Both sides can be independently programed/read from each other. For example, the HF side of my NExT is set up to send people to one of my social media links, and the LF side is programed to my work ID badge.
Reprogramming is pretty straightforward with devices like the Proxmark3 that DT also sells. I don’t know your level of programming skills, but if you can follow instructions as well as I can, this guide is your gateway to reprogramming the implant to whatever you desire.
Hopefully this helps!