You need to know due to the government policies and Islamic regulation access to thousands of websites is officially blocked by the government. Currently, these websites are filtered:
BBC and most Western news services
Currently, Skype, whatsapp, Instagram are accessible, but most Iranians use telegram.me or whatsapp to communicate with each other. Many, perhaps even most, Iranian businesses in the tourist sector have an Instagram page. To get around filtered websites, most Iranians use a VPN client – set one up on your device before you leave home, although it can slow things down considerably, which can be particularly frustrating where the wi-fi is already slow.
Attention: Try not to use internet banking or even PayPal while you’re in Iran, as international banking sites routinely block any IPs coming from Iran.