Moscow - April 30, 2003 - Mobile TeleSystems OJSC ("MTS" - NYSE: MBT), the largest mobile phone operator in Russia and Central and Eastern Europe¹ today announces that it has decided to exercise an option agreement with Ukrtelecom to acquire an additional 26% stake in Ukrainian Mobile Communications (UMC).

On April 28 2003, MTS notified Ukrtelecom that it would be exercising its option in respect of a 26% stake in UMC pursuant to the terms and conditions of the call option agreement signed on November 5, 2002. According to the agreement, the purchase price for the stake will be $87.57 million and the sale is expected to occur prior to mid-June, 2003. If the transaction is completed, MTS' ownership in UMC will increase from 57.7% to 83.7%.

As previously announced, MTS acquired a 57.7% stake in UMC, one of the two leading mobile operators in Ukraine providing services to over 1.8 million subscribers, for $194.2 million from KPN (16.3%), Deutsche Telekom (16.3%) and Ukrtelecom (25%) and entered into option agreements with Ukrtelecom and TDC to purchase their respective 26% and 16.3% stakes in the company. If all options are exercised, MTS will own a 100% stake in UMC.

MTS consolidates UMC into its financial and operating results as of March 1, 2003.

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Completion of the acquisition is conditioned on satisfaction by the parties of certain conditions precedent including the receipt of consents, orders, approvals or clearance, including governmental approvals where stipulated. Substantial delay in obtaining satisfactory approvals or the imposition of unfavorable terms or conditions in the approvals could have an adverse effect on the business, financial condition or results of operation of MTS and may cause the abandonment of the acquisition and there can be no assurance as to whether or when any such additional sale will occur.

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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.
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¹ In terms of subscribers
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Mobile TeleSystems OJSC (or "MTS") is the largest mobile phone operator in Russia, and Central and Eastern Europe. Together with its subsidiaries, the company services over 9.8 million subscribers. The 58 regions of Russia as well as in Belarus and Ukraine in which MTS and its subsidiaries are licensed to provide GSM services have a total population of approximately 169.2 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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For further information contact:

Mobile TeleSystems, Moscow
Investor Relations
Andrey Braginski
tel: +7095 911 6553
e-mail: ir@mts.ru

Press Secretary
Eva Prokofieva
tel.: +7095 737 4530
e-mail: eva@mts.ru

Gavin Anderson & Company, London
Halldor Larusson
tel: +44 (0) 20 7554 1400