I don't have an iCloud account. I'm not sure what "basic functions for a smartphone" I'm unable to use, but, I don't want my photos backed up to iCloud - I'll handle that on my own, for the photos I actually want somewhere other than on my local device. Everything otherwise seems to work.
I don't use iMessage. I've ticked the little box that says to use regular SMS and not iMessage. (This was back when there were stories of people getting stuck on iMessage and losing messages when they switched to another OS, and I wasn't sure I wanted to buy into the Apple platform permanently. I could probably switch back now, since I've been a regular iOS user for years and I hear that https://selfsolve.apple.com/deregister-imessage/ works.) Multi-party SMS works fine. Multi-party Signal, Hangouts, Slack, etc. chats also work great. Similarly, I don't use FaceTime, but I've got tons of messaging apps that support video calls on their own.
Generally things have been fine, so I'm curious what specifically hasn't worked for you.