Moscow, Russian Federation — August 28, 2003 — Mobile TeleSystems OJSC (“MTS” — NYSE: MBT), the largest mobile phone operator in Russia in terms of subscribers, today completed a previously announced transaction to acquire a 50% stake in Primtelefon, a cellular operator in the Far East and Siberian regions of Russia.

MTS has completed the acquisition of a 50% stake in Primtelefon, a holder of a GSM 900/1800 license for the entire Far Eastern region and certain regions in Siberia with a total population of approximately 11.4 million covered by the license. The company’s network is already operational in the Primorsky and Sakhalin regions and the company is rolling out further operations in Amur, Khabarovsk and Irkutsk regions. Primtelefon also holds an NMT 450 license for the Primorye region. The subscriber base as of June 30, 2003 was around 74,000 (69,000 on GSM networks and 5,000 on NMT networks).

As reported earlier, the transaction to acquire a 50% ownership in Primtelefom is a part of a series of related transactions in which MTS has acquired equity interests in five regional mobile phone companies from MCT Corp, a Delaware corporation for a total of $70 million.

The completion of the acquisition increases MTS’ license footprint to 72 regions and the population covered by the license to 184.1 million.

¹ Regions of Russia under the license are: Sakha (Yakutia), Khabarovsk, Primorye, Amur, Magadan, Sakhalin, Irkutsk, Chita regions, Evreysky, Chukotka, Kamchatka, Ust-Ordynsky Buryatsky, Aginsky Buryatsky, and Koryaksky autonomous regions, as well as the Republic of Buryatiya.

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Mobile TeleSystems OJSC (or “MTS”) is the largest mobile phone operator in Russia and Eastern Europe in terms of the number of subscribers. Together with its subsidiaries, the Company services over 12.8 million subscribers. MTS and its subsidiaries are licensed to provide GSM services in 61 regions of Russia, in the Ukraine and in Belarus, which together have a total population of approximately 172.7 million. Since June 2000, MTS’ shares have been listed on the New York Stock Exchange with the ticker symbol MBT. Additional information about MTS can be found on MTS’ website at www.mtsgsm.com.

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Some of the information in this press release may contain projections or other forward-looking statements regarding future events or the future financial performance of MTS, as defined in the safe harbor provisions of the U. S. Private Securities Litigation Reform Act of 1995. You can identify forward looking statements by terms such as “expect,” “believe,” “anticipate,” “estimate,” “intend,” “will,” “could,” “may” or “might” the negative of such terms or other similar expressions. We wish to caution you that these statements are only predictions and that actual events or results may differ materially. We do not intend to update these statements to reflect events and circumstances occurring after the date hereof or to reflect the occurrence of unanticipated events. We refer you to the documents MTS files from time to time with the U. S. Securities and Exchange Commission, specifically, the Company’s most recent Form 20-F, as amended. These documents contain and identify important factors, including those contained in the section captioned “Risk Factors,” that could cause the actual results to differ materially from those contained in our projections or forward-looking statements, including, among others, potential fluctuations in quarterly results, our competitive environment, dependence on new service development and tariff structures; rapid technological and market change, acquisition strategy, risks associated with telecommunications infrastructure, risks associated with operating in Russia, volatility of stock price, financial risk management, and future growth subject to risks.

For further information contact:

Mobile TeleSystems, Moscow
Andrey Braginski, Investor and Public Relations
tel: +7 (095) 911-65-53e-mail: ir@mts.ru