Mobile devices don't page because killing a process on a device which is usually only showing the user one thing at a time, due to want of memory, isn't usually that big of a deal.
iOS does have VM though, and apps use it to implement home brew memory paging. Obviously not useful for the stack, so it encourages more explicit memory management. The mmaped region is bizarrely counted towards the total, leading to windowed memory schemes from the 1960s, where mmaps are remapped to access different chunks of data. Some poor design choices.
Also, app code is paged in, it just doesn't need to be paged out.
