Worst. Article. Ever. Having just been in the situation of being a large corporation client trying (successfully) to hire a firm to do this, I'd like to point out that everything you've said about the prep here is just wrong.

(1) Big infrastructure needed: Seriously, if the client is not picky, you should be able to build a working basic infrastructure for the back end in a week. And that's generous.

(2) You need a way to communicate: The claim that there is no standard way to do it is just plain wrong. There is absolutely a standard way, its how everyone with a brain does it these days, and its easily supported through every device SDK - you use HTTP

(3) Design the API: No, design the app. Then determine what question it needs to ask the server, and figure out how to make the server answer them. Designing the API first is a very engineer thing to do - if you're the only user for the API its just a flat-out wrong approach

(4) Pay for it: Sure, but I'll pay for the amount of time it should take to do this. Which is a week. Engineers that want me to pay for them to sit and write 200 page requirements specifications need not apply. I want to work with the people that want to build something on day 1, and then keep tweaking it.