The iPhoneOS doesn't ship with dynamic_pager, which implements user-space allocation and enabling of page files, but in theory, the necessary kernel support should be available.

Enabling paging to a specific file is done via the macx_swapon syscall:

http://fxr.watson.org/fxr/source/bsd/vm/dp_backing_file.c?v=...

dynamic_pager handles allocation of swap files on-demand (requires free ADC account):

http://www.opensource.apple.com/darwinsource/10.0/system_cmd...