Just ran across this. Can't say as I find one claim more or less believable than the other without corroboration from some other sources.
A contradictory statement from Russia:
Russia Denies Weapons Sale to Iran
MOSCOW —
Russia is not selling
Iran an advanced air-defense system, Russia’s agency for monitoring international defense cooperation said in a statement on Monday, refuting claims by an Iranian official reported Sunday that the system was already being delivered.
“Military-technical cooperation with Iran is conducted on a planned basis corresponding with agreements signed earlier and in observance of all international obligations,” the agency, the Federal Military and Technical Cooperation Service, said in a statement posted on its Web site.
“Information that has appeared in several media outlets about deliveries of the S-300 anti-aircraft system to Iran does not correspond to reality,” the statement said.