Anecdotally, VPNs are incredibly popular in Iran and the government hasn't had a great deal of success in blocking their usage. Unlike the Chinese GFW, the government entities in Iran that want to run a nationwide firewall are not able to attract the 'best and brightest' network engineers. The sort of Iranians who might be qualified to implement such are not living in Iran, they're living in Los Angeles and working for six-figure salaries in US dollars.