iOS developer should have command over various languages and various tools for the iOS application development. They should have mastery over Objective C, C++, etc. They should have command over x-code for coding and Interface Builder for designing interface for application. If they have to develop games then they should be accustomed with Cocos2d and Unity 3D. Moreover they should know Core animation and Core images, OpenGL, etc.
Apart from technical glitches they should be fluent at communication and have understanding of different culture and different practices prevailing in different businesses so they can grasp the concept of the clients and speak their language to convince the clients. iOS application developer should use the latest technology for communication like e-mail, instant messengers (including video chat), live chats on the website and telephone conversation. Developer should follow standard development process and have good project management ability so he/she can provide regular updates to the clients regarding to the development. Time zones are big constraints for outsourcing work so developers have to overcome it at any cost.