The announcement raises the voting shares held by Altimo to just above that controlled by its Norwegian rival Telenor and extends a bitter feud for control of a company with the world's six-largest mobile subscriber base.
The telecoms investment branch of Fridman's Alfa Group said it acquired the 14.8 percent stake from the Egyptian investor's Weather company and bought additional shares on the open market to raise its holding to 40.5 percent.
That just edges the 39.5 percent Norway's global wireless operator achieved earlier this year thanks to a deal with Sawiris that is now being contested by Russia's anti-monopoly authorities.
The New York-listed Vimpelcom Ltd. -- famous for the brands Beeline and Wind -- closely trails MTS and MegaFon in Russia and is a strong presence on the Italian market.
It reported a jump in second quarter profits to $488 million on Wednesday thanks to favourable currency exchange rates and continued revenue growth in its Russian divisions.
But the company has seen its stock take a 25-percent hit in recent months as court battles leave management stranded and forced to defer lucrative dividend payments to investors.
The Financial Times said Wednesday that the legal battles had also forced Vimpelcom to indefinitely postpone a planned European listing that was aimed primarily at broadening its investor base.
Yet Vimpelcom's American Depository Receipts (ADRs) were still ending a volatile day of New York trading up more nearly 10 percent on news of the Altimo deal.
Investors appeared to be banking on the idea that a truce will soon settle over the company that sees Telenor and Fridman's unit share an equal number of board seats and in effective joint control of the firm.
It was not immediately clear how Telenor intends to respond to the latest move by one of Russia's original and most powerful oligarchs -- a man who has previously challenged the Kremlin over a big Arctic oil deal and won.
The Norwegians have fought with Fridman over Vimpelcom's operations in Ukraine and its current struggles in Russia have become a part of official government contacts between Moscow and Oslo.
But Fridman's latest business move is in step with Russian government thinking that would see mutual operation of Vimpelcom by the two enemy camps.
Thursday's edition of the Kommersant business daily said Russia's Federal Anti-Monopoly Service (FAS) had come up with four-point peace pact under which Telenor would not fight Fridman's efforts to win parity ownership in Vimpelcom.
The accord -- terms of which would in turn approve the Norwegian's own acquisition of the Egyptian tycoon's 11.4-percent stake -- would also require Telenor to agree to a Russian chief executive for the phone operator.
Kommersant said that Prime Minister Dmitry Medvedev's official spokeswoman Natalia Timakova had confirmed the outlines of the proposed compromise.