Defense Secretary Robert Gates said today that "the opportunity for success [in influencing Iran] is probably more in economic sanctionsthan it is in diplomacy. … What gets them to the table is economic sanctions." Earlier, Gates warned Iran in Obama's behalf:

at a conference in Bahrain...

"The president-elect and his team are under no illusions about Iran's behavior and what Iran has been doing in the region and apparently is doing with weapons programs...So anyone who thought that the upcoming months might present opportunities to test' the new president would be sorely mistaken...President Obama and his national security team, myself included, will be ready to defend the interests of the United States and our friends and allies from the moment he takes office on Jan. 20."

more from the transcript:

"I bring from President-elect Obama a message of continuity and commitment to our friends and partners in the region. ...More extensive planning has been done across the government in preparation for this transition than at any time I can remember and I have worked for seven presidents, soon to be eight. So anyone who thought that the upcoming months might present opportunities to "test" the new administration would be sorely mistaken. President Obama and his national security team, myself included, will be ready to defend the interests of the United States and our friends and allies from the moment he takes office on January 20th.
...Unfortunately, no discussion of the security situation in Iraq is complete without mentioning Iran, a country whose every move seems designed to create maximum anxiety in the international community.
There is no doubt that Iran has been heavily engaged in trying to influence the development and direction of the Iraqi government and has not been a good neighbor. Much of that effort has been focused on training and supplying groups intent on undermining the government more often than not through violence and attacks on Iraqi security forces and government installations and officials. Of course, the use of sub-national actors as Iranian proxies should be no surprise considering the financial and military support that Tehran has long given organizations like Hamas and Hezbollah, which also seek to undermine legitimate governments by violent means.
Now, when it comes to Iran's missile programs, we all know that pictures can be deceiving. Even so, it is clear that Iran has, this year, tested long-range missiles that can hit any country in the Middle East. At the same time, Iran has continued its pursuit of a nuclear program that is almost assuredly geared toward developing nuclear weapons. The last thing this region or the world needs is a nuclear arms race in the Middle East.
So what can be done about Iran? For starters, the international community has come together and has increased pressure on Iran diplomatically and economically. I encourage you to implement fully the financial measures called for by the United Nations."

Manama Dialogue (Bahrain)
As Delivered by Secretary of Defense Robert M. Gates, Manama, Bahrain, Saturday, December 13, 2008