We got our Iranian Tourist visas in Turkey with limited hassle. When you get within a week or so from Erzerum you can e-mail email@example.com
(a travel agency in Tehran). They will need from you the following:
a) a list of places you will want to visit in Iran (just make up a list of common towns using a map)
b) $80 dollars tranferred to their bank account (and faxed proof of this if you want to speed things up - we used the AKBank in Ankara who even sent the fax for us but the tranfer fee was about $15)
c) a completed form (they will send you this by e-mail) with passport details etc
The visas were organised within a week and we collected them in the Iranian Consulate in Erzerum. To collect them you need two photos and to pay $72 dollars.
Take note that your visa will start 'ticking' the day you collect it so wait until you are ready to leave Erzerum. The Tourist visa lasts one month but can easily be extended once in Iran.