There are a few steps in order to have mobile continuous integration working.
The easiest possible Continuous Integration (CI) setup is with one dedicated build machine. Some CI software allows to separate CI management part (i.e. Jenkins master) and execution (i.e. Jenkins slaves).
You have to choose, what operating system you should use as host of your installation. For iOS projects, it should be OSX host since (it allows build both iOS and Android projects). In case you want to build only Android projects, you can use most modern Linux flavors.