Is there any way to simulate airplane mode in the iPhone Simulator?
You could install Apple's Network Link Conditioner
On Yosemite:
Network Link Conditioner can be found in the "Hardware IO Tools for Xcode" package. This can be downloaded from the Apple Developer Downloads page. Once the download has finished, open the DMG and double-click "Network Link Condition.prefPane" to install (source).
With this preferences panel you could create a profile with 0kbps speed.
On older versions of OSX:
Mountain Lion / Mavericks: Xcode > Open Developer Tool > More Developer Tools
Lion: /Developer/Applications/Utilities/Network Link Conditioner