Rice's decision to send Burns to Geneva was a sharp departure from the usual U.S. policy, which has been not to talk to Iran about its nuclear program until Tehran gives up uranium enrichment work the West believes is aimed at building an atomic bomb. Iran says it is for peaceful power purposes.
source: the sixth paragraph of
http://uk.news.yahoo.com/rtrs/20080719/tpl-uk-iran-nuclear-19346ad.html