I finally got everything I need for my first few devkits. I've learned a few things from making these, that will hopefully make the final product much better.
1. Have a way of flashing the stock firmware onto the chips
This seems like a no-brainer, but unfortunately I made the stupid mistake of not including an ICSP header for writing the bootloader to the CPU, so that has to be done with some thin wire on these ones. Oops.
2. The easiest method may also be the cheapest
The buttons I used LOOKED like they'd be the cheapest option to go with (they had a minimum amount of 1) but were WAY too much money in hindsight. I took a look at the buttons the software I'm using, and they would have saved me a dollar per devkit. Doesn't seem like a whole lot, but when I'm trying to build (and turn a profit on) a $75 device, every penny counts.
3. Breaking things down into smaller pieces is actually really good advice
I wasn't thinking a whole lot about what a phone really *needs* when I built these devkits. They can't charge batteries, they don't have actual cellular (but that one wasn't my fault!) and overall, they're basically what I already had, but in a nicer package. If I had sat down and thought about what every single part of a phone was for, I think I would've ended up with a better set of devkits.