IranCell is pretty good. They have good coverage around the country and 4G in most major cities. We had various Iranians bending over backwards to help us with all kinds of stuff, including the SIM cards. It's an amazingly hospitable country.

I hear this a lot, but it isn't entirely correct. You cannot officially get cash once you are in. But like with everything in Iran the people have come up with all kinds of creative ways around the rules/limitations.

You can get cash with a credit card or a Paypal account. In Tehran go to the many exchange offices near Ferdowsi square and look for one with small logos of the above payment services. They will not let you make a withdrawal there, but will send you to a flat in some inconspicuous apartment building filled with computers on permanent VPN connections to the outside world. You do an online payment, they give you cash, either USD or Rials.
It does require a certain amount of trust in the people you are dealing with and they will charge you a commission of around 10%.
In the tourist places (Esfahan, Shiraz, ...) some of the carpet shops also do it.

But it's still better to make sure you have enough on you when you enter the country. If you don't like walking around with a lot of cash, go to a Meli Bank and ask for a "Tourist Card". They'll make you a temporary bank account, you can deposit whatever sum you like and get a debit card. There's one at the Imam Khomeini Airport in Tehran, in case you're flying in. You'll get the remaining money back when you close the account.

__________________
Belgium to Nordkapp via Iran | Discover Overland | Destination World