As far as I know iOS dealt with memory by ruthlessly ejecting background apps from memory as needed. If your foreground app exceeded memory limits and all background apps had already been freed then your foreground app is killed.
The latter is pretty rare given how much work has been put into notifying apps about memory pressure, making them easily suspend/resume, and not using garbage collection.
Well, in a way it is a form of swap (just a program-controlled one over an automatic), to tell it to save its state because it is gonna be killed. And to be honest, it is a very fair way of working that should be moved to the desktop as well (plenty of apps have no reason to run in the background - though memory eviction is not needed there when ample memory is available).
Also, sorry to be pedantic but reference counting is a garbage collector algorithm, but I do understand what you mean here (RC needs less memory at the price of not being able to defer work to a concurrent thread)
The latter is pretty rare given how much work has been put into notifying apps about memory pressure, making them easily suspend/resume, and not using garbage collection.