BERLIN, Sept 7 (Reuters) - Softbank said on Tuesday it had gained access to future gains in the Deutsche Telekom share price through a complex share-swap deal under which the German group will raise its stake in U.S. unit T-Mobile. “I’m a big believer that Deutsche Telekom stock has material upside in the future,” Softbank executive Marcel Claure told a briefing. As part of the $7 billion deal announced earlier, Softbank will exchange T-Mobile shares under a fixed-price option deal for a 4.5% stake in Deutsche Telekom, which Claure described as significantly undervalued. (Reporting by Douglas Busvine, editing by Emma Thomasson) Our Standards: The Thomson Reuters Trust Principles.