Iranian government, has started the eVisa plan.
It means all visitors can apply for their Visa through the web. The official website for Iranian eVisa plan is located at
http://evisa.mfa.gov.ir:7780/mfa/
On May 2009, the site is working.
As rules and procedures for this eVisa may change, it is highly recommended to check the latest regulations, before taking any actions. This page will provide latest information on the plan and requirements.
Official website for Iranian Ministry of Foreign Affairs, could be checked as another source for any updates or changes in plans.
Visitors from certain countries, (there are some exceptions, like UK, USA, Sumalia, Iraq, Afghanistan, etc..), can obtain a Visit (short-stay) visa on their arrival to Iran, on certaing entry points, including Tehran Imam Khomeini Airport, for 15 days of stay.
To obtain this visa, You need to have a copy of your passport (having a copy of your passport first and second pages is recommended) and 2 passport photos, plus 50 euros (or equivalent) and Name , Address and Phone number of a host in Iran (a booked hotel is not acceptable at this time, a person or a company is required as you host)
Direct Phone numbers to the tourist visa office in IKA ( Tehran Imam Khomeini Airport) is (+98 21) 44666830 and 44667210