Most Iranians have squat toilets at home, but the majority of better hotels have thrones or a choice of loos. Almost all public toilets are squats and while some are regularly cleaned, others are very definitely not. Still, there are usually enough options that you won’t have to enter anywhere too stinky. Mosques, petrol stations, bus and train stations and airport terminals always have toilets, sans toilet paper.
Fortunately, most of the ubiquitous small grocery stores stock toilet paper or tissues. All but the cheapest guesthouses now supply toilet paper too, though sometimes you’ll need to ask. That said, it’s worth remembering that the wise traveller carries an emergency stash of TP. Whatever you use, most plumbing is not designed for paper so put your used sheets in the bin not the bowl.