[Rails] ruby on rails server application with iPhone / Android IOS client? best practice how to begin...

Very interested in IOS and perhaps later Android client that connects to my
ruby on rails server app.
What are good resources, books, tutorials, blogs to check and dive in as a
ruby developer want to develop a simple client to begin with, who has
experience on this topic and can share some insights?

In the basics my IOS client will be a client for the rails app wich is in
basics just a simple social media site with just profiles and images I
would like to list, later on I want to add messaging but for now get the
basics and learn how this should work.
I have a bit of knowledge of objective C and a little bit of experience
with Xcode and the basic principles, So I'm not a total Newbie on this.
Whats so unclear is how to "Connect" Rails app <--> IOS client.


* Advised is not to use general rails app controllers(?) so you write a set
of "iPhone" controllers instead?
* Are there any write-ups on how to start with Xcode for connecting it to a
rails app?
* Books, Ebooks, Blog posts anything to get you started?
* Commercial "starter kits or screencasts to buy to get you up and running
fast based on professional best practice methods ? "
* You use JSON / XML to communicate?
* For login I use devise, heard its hard to implement in IOS clients ( In
basics I will leave login out )

Any other thoughts on this matter? Would love to learn how to write a cool
IOS client for my Rails app.
Hope someone can get me and other future newbies to this matter on "Track"
;)