You can easily pickup RoR if you get into a situation where you have to use the framework.

However, if you're like me and you know javascript well, Objective-C might be the better choice. I've recently gotten into iOS app development and started off with using Phonegap. However, I quickly ran into the limitations of Phonegap and started having to do minor Obj-C modifications to get one of the apps to do things I needed. This experience has lead me down the path of deciding to tackle Obj-C, which for me is the better move than learning Ruby.