Moscow, Russian Federation – Mobile TeleSystems OJSC (“MTS” – NYSE: MBT), the leading telecommunications operator in Russia and the CIS, announces that Moody's Investors Service has downgraded MTS’s senior unsecured issuer rating from Baa3 to Ba1 following the downgrade of the Russia’s sovereign debt rating to Ba1/Not Prime (NP) from Baa3/Prime-3 (P-3). Moody's has also assigned a Ba1-PD probability of default rating (PDR) to MTS. The ratings remain on review.

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For further information, please contact in Moscow:

Joshua B. Tulgan
Director, Department of Corporate Finance and Investor Relations
Mobile TeleSystems OJSC
Tel: +7 495 223 2025
E-mail: ir@mts.ru