Is the internet in Iran heavily censored? Will I need a VPN to use WhatsApp, Instagram, or Google?

Yes, you absolutely will. This is the most important thing to know. Iran's government operates a "Great Firewall" that blocks all major Western apps, including WhatsApp, Instagram, Facebook, Google, YouTube, and X (Twitter). A Cellesim eSIM will give you a data connection to a local network (like Irancell/Hamrahe Aval), but it does NOT bypass this state-level censorship. To use any of these apps, you must install a high-quality, paid VPN on your phone before you arrive in Iran.