The German telecoms group and its partner, British startup Stratospheric Platforms, said that a remotely piloted aircraft flying at 14,000 metres (45,000 feet) had successfully connected with its terrestrial 4G network from an on-board antenna.
The airborne base station, which can cover an area up to 140 km (87 miles) across, handled voice and video calls, data downloads and web browsing from a smartphone user on the ground during trial flights this month.
"We won't stop until everyone is connected," Deutsche Telekom CEO Tim Hoettges told a video presentation on the project, which has been in development for the past five years.
"A stratospheric network can help reach areas that have been difficult to supply up to now."
Hosting base stations in the stratosphere promises the fast reaction times that next-generation 5G networks will need to support innovations such as self-driving cars.
But, while aerial antennas offer a speed and cost advantage over satellites, keeping them aloft poses a design challenge.
Alphabet's rival Loon venture uses high-altitude balloons to run wireless networks and Facebook grounded an experimental solar-powered internet drone two years ago after concluding it was not feasible.
Deutsche Telekom's test flights were staged over the state of Bavaria in southern Gemrany using an adapted H3Grob 520 propeller plane because Stratospheric Platforms is still developing its own pilotless aircraft.
The UK startup says its lightweight "platform" will have a wingspan of 60 metres - as big as a Boeing 747 - but weigh only 3.5 tonnes and be able to stay aloft for nine days.
It will use an emission-free hydrogen fuel-cell system, which can generate far more power than solar cells. The on-board antenna, weighing 140 kg, will be capable of doing the job of 200 terrestrial towers.
Richard Deakin, chief executive of Stratospheric Platforms, said the platform would make its first flight in 2022 with operational deployment expected around 2024.
Deakin said he plans to build a factory that can produce up to 200 of the aircraft a year, adding that the challenge will be to supply enough.
The startup was founded in 2014 and Deutsche Telekom came on board as an investor two years later and holds a 38% stake.
Stratospheric Platforms said it was holding talks with other potential investors to raise about 50 million pounds ($65 million) in a so-called Series B funding round. Funding to date is in double-digit millions of pounds.
Partners for its aerial platform include Northrop Grumman and Thales. It is also working with QinetiQ and others on the hydrogen power system.
(Reporting by Douglas Busvine; Editing by Jane Merriman and David Goodman)
By Douglas Busvine