Sorry, I’m on Android, no clue about iPhones. Perhaps your favourite search engine or some other Dopers may know more.
Your Wallpaper comes up on the screen whether you’re logged in or not, so you’ll want to put the pertinent info on your wallpaper. I’m not going to go into how to make an image with text on it, but that’s what you’ll need to do. I don’t see anywhere in Wallpaper Customization where you can add text (although it looks like the ability to do so is in the works).
So basically make an image with text on it, set it as your wallpaper.
Well, crap, I can do that with one thumb! Easy peasy! (I can “annotate” or “markup” a photo with text across it). I could just do that with the basic photos on my old iPhone, or use Preview on any old Mac. Or get fancy and do it in Photoshop.
Thanks for the $300. Came in handy.