1. Locating other trainers with a Poryphone
The Poryphone can locate other trainers (players) around you in a 4 chunk radius who have Location turned on and if their phone is set to Online (Online is available, Do Not Disturb will not show Location, and Offline is all features of the phone are off)
This idea is most likely my favorite, as you can chat with poryphone owners through another form of chat. It's a pretty simple idea, but it's one that makes it much cooler and is like a real phone.
The Camera (item) would be unneeded after this being added with a camera in the phone, so the new function for the old Camera would be for the exact same purpose it serves now: Photographing Pokemon for Pokemon Frames. The New Camera included with the Poryphone would allow you to take pictures (same sort of thing as the Camera Item) and post them in the messaging service said above. (It would be like taking a screenshot with F1 hiding the UI)
4. Other Features
Some extra features would be Theme/Background Color, Font, and the most important feature of a phone, a battery. By bringing back the Cell Battery recipe to craft it, and putting two batteries in the middle row and an Iron Ingot in the middle, it would craft an infinite battery pack, which when right-clicked, would add to your phone, making the charging station (Don't have a Recipe in mind, so make one up) unnecessary.
I hope that you like this idea!,
Note: C = Cell Battery, A = Air (Nothing There), and I = Iron Ingot
A A A
C I C
A A A [This is the crafting recipe found in section four.]