If they're physically removing access to the Internet, the only way around it would be to physically restore access, which isn't exactly a matter of breaking through some firewalls or firing up Tor.

The only realistic way I could see this working on a large scale is a very wealthy, motivated, and low-profile hacker somehow managing to string in fiber across the border from neighbouring countries, set up multiple wireless access points, and get a mesh network going across the country.

On a small scale (say, for a hacker and his buddies or an underground resistance force), I suppose you'd only need to get a decent wireless-N access point near the border (in Turkey, perhaps?) broadcasting a WPA-encrypted hidden network, then have specific people in strategic locations running cheap wireless-N routers configured with Tomato or DD-WRT to act as repeaters. Obviously this isn't foolproof (hidden networks are easy to find if you're looking for them), it would be easy to cut off if it were discovered, and it would be slow as balls, but if you could manage to get a large enough chain going everywhere it needed to be, and its use were coordinated well enough to ensure that it would only be used in urgent situations (and only through Tor), then it could prove to be an invaluable resource.

But yeah, Iran's people need another revolution, fast.

»The only realistic way I could see this working is....stringing fibre across the border

Or satellite Internet.

Dialup, unless voice lines are dead.

Ah, yeah, I thought I brought that up but evidently not. Yep, satellite would definitely be an option, but somehow I feel like that would need to involve opposition powers beyond even a wealthy hacker in Iran.

Can Iran block satellite internet? Maybe US drones can "airlift" Wi-Fi access as the Internet Age's "Radio Free Iran."

That would be interesting. We tend to think of resistance coming from within with these sorts of things, but it would really be something to see another nation (or private entity) begin a blatant campaign of getting Internet access into Iran in every way possible (super-powered Wi-Fi and 4G blasted all along the borders, free unrestricted satellite Internet to everyone who owns or can ghetto-rig a dish, millions of concealed mesh-networked routers all over the country (with dishes attached), thousands of proxies to the Internet planted within the Irantranet, etc.).

Edit: justincormack brought up an awesome point too: dialup. If we could get a black market for high-compression modems going, and possibly use the modems to fortify the mesh network routers as a secondary Internet source to the satellite dishes, this could end up being fairly robust.

I would love to see the CIA or some other organisation put a few billion into this if Iran really goes through with the plan.

Supposedly, they'll still have an Intranet, it should be possible to tunnel internet connections over it to some hidden bridges.