The website of Uzbek national railway UTY has a news story about the recent agreement with Islamic Republic of Iran Railways. Google’s translation from Russian gives:
30-10-2008 October 28, TG
Tehran had a meeting and talks executive director of Iranian railways, Hassan Ziyari with the chairman of the board GAZHK Uzbekistan Temir YULLARI Achilbaem Ramatovym.
At the meeting the parties focused on specific issues expand bilateral cooperation in rail transport. In particular, the parties agreed on the establishment of private transport companies, which will transit rail transport, and joint investments in rail transport corridor project, which will link the railways of Iran and Uzbekistan through Afghanistan.
Source: UTY
Iran’s Press TV gives more details:
Iran, Uzbekistan sign railway pact
Thu, 30 Oct 2008 23:30:25 GMT
Iran and Uzbekistan have signed a nine-article cooperation pact on railway cooperation after holding a two-day meeting in Tehran.
The agreement was finalized between the managing directors of the national railway companies of Iran and Uzbekistan Thursday.
The pact includes initiating a container train transit route between Almaty, Tashkent, and Istanbul, launching a container train route between Tashkent and Bandar Abbas, a 25 percent discount to be granted to Iran for using Uzbek carriages, the passage of Iranian railroad cars through the Uzbek network and settling outstanding accounts between Iran-Uzbekistan railways
[…]
“Establishing private transit transportation companies and joint investments in launching railway networks among Iran, Afghanistan, and Uzbekistan will allow Uzbekistan access to the Persian Gulf waterway,” Ziyari added.
[…]
While looking for more information, I came across Helmut Uttenthaler’s Trains in Uzbekistan blog.