Also in 1986, Obermann founded his own company ABC Telekom (now The Phone House Telecom GmbH), located in Münster, Germany.

After having sold his remaining shares, Obermann started his career at Deutsche Telekom Group, first at T-Mobile Deutschland GmbH as a Member of the Executive Board.

During Obermann's tenure as CEO, he was instrumental in obtaining an exclusive partnership from Apple Inc. for Deutsche Telekom to sell the original iPhone in Germany and in other European countries in late-2007.

[10] Obermann left Deutsche Telekom in December 2013 and assumed the role of CEO of the Dutch cable and internet provider, Ziggo.

In February 2015, Obermann became Partner and Managing Director at Warburg Pincus International LLC.