Net profit fell by nine percent to €475 million ($625 million), while adjusted earnings before interest, tax, depreciation and amortization (Ebitda), its benchmark, lost five percent to €5.01 billion, a statement said.
Deutsche Telekom and France Telecom have set up a joint venture with their respective mobile operations in Britain, T-Mobile UK and Orange UK.
The former's results are thus no longer integrated into Deutsche Telekom's figures, a factor in a four percent drop in sales to €15.53 billion.
When that development was stripped out of the calculation, group sales gained a slight 0.9 percent, Deutsche Telekom said as it welcomed a stabilisation of its domestic market.
The former German monopoly has been faced with a flood of fixed line clients cancelling their contracts. Fixed-lines sales decreased by 2.9 percent in the second quarter, the slowest decline since 2008, the statement said.
Around 1.7 million clients have dropped such service in the past year, however.
Sales of the group's T-Mobile USA division gained seven percent over the same period meanwhile, a welcome stabilisation amidst tough competition in one of Deutsche Telekom's most important foreign markets.