German telecom operator Deutsche Telekom on Wednesday reported record profits for 2019, with US unit T-Mobile gleaning millions more customers ahead of a merger with competitor Sprint.

The bottom line bounded almost 80 percent year-on-year to 3.9 billion euros ($4.2 billion) making 2019 "the most successful year in the history of the company", Deutsche Telekom said in a statement.

The operator was now the "clear number one in our industry in Europe", it added.

Piling 'em high: Client numbers at T-Mobile were up by 6.4 million
Piling 'em high: Client numbers at T-Mobile were up by 6.4 million GETTY IMAGES NORTH AMERICA / JUSTIN SULLIVAN

For 2020, Deutsche Telekom said profit from operations was likely to be stable, and sales on the rise, even without counting in the effects of the Sprint-T-Mobile tie-up.

Years of rapid growth in its American subscriber base meant T-Mobile already accounted for around half of the group's 80 billion euros in annual turnover in 2019, compared with just over a quarter for home market Germany.

With the Sprint takeover, recently given the go-ahead by a federal court, the company's US subscriber numbers will leap to over 100 million.

Bosses say that will give T-Mobile the scale to compete with the sector's giants Verizon and AT&T.