Deutsche Telekom said on Friday Blackstone's stake had fallen to 2.93 percent on November 6.
Blackstone declared in early August that its shareholding in Deutsche Telekom was 4.44 percent.
Based on Deutsche Telekom's closing price of 8.60 euros on November 6, the 65.2 million shares sold by Blackstone were worth around 561 million euros ($713 million).
In April 2006, Blackstone bought 192 million shares in the company from the state-owned development bank KfW KFW.UL at 14 euros per share, for a total of 2.68 billion euros.
The 65.2 million shares at that time would have been worth nearly 900 million euros.
A spokesman for Blackstone declined comment to Reuters.
Deutsche Telekom's biggest shareholder is still the German government, which owns a 15 percent direct stake and a 17 percent indirect stake, which is held by KfW.
Deutsche Telekom on Thursday stuck to its 2012 profit and dividend outlook as its third-quarter core result was ahead of expectations, fuelled by its German activities.
($1 = 0.7868 euros)
Reporting by Alexander Huebner and Joern Poltz; Writing by Marilyn Gerlach; Editing by Mark Potter