All other things being equal, is it easier/quicker/more flexible for a US citizen to get a business or tourist visa if going to Iran for 2-3 weeks? Aside from a letter of invitation for a business visa, are there different requirements? If the trip is a combination of business and pleasure, which visa is recommended? The business would be unpaid, something a bit like volunteer work.
Sorry in advance if this doesn't fully answer your question. I only have experience in getting a tourist visa to visit Iran. My travel was arranged by a company here in the United States who obtained the visa authorization number needed to apply for the visa. Residing in the Northeast, I took the train to DC to drop off my application and passport at the Iranian Interest Section. Once they accepted my paperwork, it took about 10 days to receive the passport back via Fedex with the Iranian visa inside. My tour in Iran consisted of 10 days visiting four cities--Tehran, Shiraz, Yadz, and Esfahan. almost 7 years ago