I wouldn't do this if I were you. NXT 2.0 is a part-synthetic part-natural wax and contains stuff that's safe to stay on car's paint and not on your hands (and into your mouth).
Look up the Material Safety Data Sheet at
http://www.meguiars.com/msds/msds_search.cfm for NXT 2.0... for example, Hydrotreated Distillate (i.e. petroleum). So there are two ingredients that are listed as "R65: Harmful: may cause lung damage if swallowed". The other one is "R38: Irritating to Skin" (Xi means irritant). Xn stands for harmful.
I don't know how much of these chemicals stay on the phone after you buff it out, but I wouldn't take my chances. Stuff can get ingested through eating or smoking.
I'd also be careful with the metal polish. You typically want to wear gloves when using it, work in a ventilated area (e.g.
safety tips for metal polishes). You probably won't be making a huge mess polishing an iPhone case, but you want to keep your skin away from that stuff and the little metal particles that come off. After polishing, I'd wipe it down with some isopropyl alcohol to get it clean.