UPI is reporting that the Foundation for Democracy in Iran (FDI) claims that Iran will test a nuclear device this Spring, before the Iranian New Year (March 20th). FDI is, of course, a US-funded resistance group inside Iran. This means that they may realistically have access to this kind of information, and that their motive for such a statement (and its veracity) is highly suspect. It reminds me very much of the kind of "intelligence" that the US got from Ahmed Chalabi about Iraq's "Weapons of Mass Destruction." Never the less, it's a scenario that is worth thinking about.
I think it's doubtful that Iran has managed to produce an atomic bomb domestically. However: we do know that Iran has a long-standing and clandestine arms-trading relationship with North Korea. We do know that Iranian ballistic missile technology has been aided by North Korean expertise from their No-Dong and Taepo-Dong programs. We do know that there have been several Iranian IL-76 flights in the past two years that have delivered and received unknown but mysterious cargo. We do know that China has on more than one instance refused overflight because of the nature of that cargo, without stating what the cargo actually was. We do know that North Korea has, most likely, several small atomic bombs. We do know that North Korea is led by a rather unstable individual. We do know that Iran has many things that North Korea wants--hard currency not being the least of these.
Is it really much of a leap from there to suggest that Iran has purchased one or more atomic weapons from North Korea? I certainly haven't heard any direct evidence to this effect, but it doesn't seem that unreasonable.
Of note: US Air Force WC-135 aircraft would be deployed to the region immediately after the detection of any Iranian test, and they are able to capture quite small quantities of nuclear radiation from such a test--even from a well planned underground test. Since isotope breakdown forms something akin to a fingerprint, it should be possible to definitively say that any Iranian bomb test used nuclear material from a North Korean reactor--if that is the case. We have samples for comparison from when the IAEA was operating in North Korea.