April 22 (Reuters) - Deutsche Telekom is

exploring a deal to combine with its U.S. unit, T-Mobile US ( TMUS )

, according to sources, in what would be a

record-breaking public merger.

The deal would crown a quarter century of maneuvering that

transformed an American upstart into a $218 billion juggernaut

and made the U.S. business the crown jewel of its German parent.

Here are milestones in the relationship between Deutsche

Telekom and T-Mobile:

1999 - Western Wireless spins off its VoiceStream Wireless

unit into the VoiceStream Wireless Corporation.

2000 - Deutsche Telekom agrees to acquire VoiceStream

Wireless and U.S. GSM operator Powertel. The deal is valued at

approximately $50.7 billion at the time of the announcement.

2001 - Deutsche Telekom completes its acquisitions of

VoiceStream and Powertel, forming what it calls the world's

first transatlantic wireless communications operator using the

GSM standard. VoiceStream becomes part of T-Mobile

International, Deutsche Telekom's mobile subsidiary.

2002 - VoiceStream, rebranded as T-Mobile USA, begins

rolling out the T-Mobile brand in major western U.S. cities,

including Las Vegas, Los Angeles and San Francisco.

2011 - AT&T ( T ) announces plans to purchase T-Mobile US ( TMUS )

for $39 billion, but the deal collapses after the intervention

by U.S. antitrust regulators. Deutsche Telekom receives $4

billion in breakup compensation.

2013 - T-Mobile USA merges with MetroPCS. The combined

company begins trading under the name T-Mobile US ( TMUS ) and the ticker

symbol TMUS on the New York Stock Exchange on May 1.

2020 - T-Mobile US ( TMUS ) completes an all-stock merger with Sprint

valued at $26 billion. Deutsche Telekom's stake in T-Mobile US ( TMUS )

shrinks to 43%, while Sprint's owner, Japan's SoftBank,

takes a 24% stake.

2021 - Deutsche Telekom sells T-Mobile Netherlands for 5.1

billion euros, or $6 billion in today's exchange rate, and uses

some of the proceeds to buy back T-Mobile US ( TMUS ) shares.

2022 - Deutsche Telekom acquires 21.2 million T-Mobile US ( TMUS )

shares from SoftBank for $2.4 billion, increasing its stake to

48.4%.

2023 - Deutsche Telekom surpasses a 50% stake in T-Mobile

US ( TMUS ). During a Deutsche Telekom general meeting, CEO Tim Hoettges

says that the company had been pursuing a majority stake since

2021.

2026 - Deutsche Telekom is exploring a deal to combine with

T-Mobile US ( TMUS ) to create a $400 billion telecoms giant in what

would be the largest-ever public merger, two people familiar

with the matter say.

($1 = 0.8515 euros)

(Reporting by Leo Marchandon in Gdansk, editing by Thomas

Seythal)