Not sure about an accent, but it will be noticeable.
From personal experience: I am aware that I often use structures specific to my current English-speaking region while speaking one of my native languages. Also, my slang and cultural references are really outdated. So I do not have an accent exactly, but it would be possible to tell something is off.
I've only seen a post about Volla and Fairphone supporting VoLTE, but if it works for OnePlus, and in the US, that is amazing!