* Still has $33/share bid from France's Iliad
* German group earns about 20 pct of profit in U.S.
* T-Mobile US has good commercial momentum - analysts
* DT shares fall as much as 5 pct, Iliad down 3.9 pct (Adds market reaction, comment on Dish's interest in T-Mobile)
By Harro Ten Wolde and Arno Schuetze
FRANKFURT, Aug 6 (Reuters) - Deutsche Telekom must decide whether to stay in or leave the United States now that its preferred strategy of selling T-Mobile US to its bigger rival Sprint Corp has crashed into a regulatory wall.
Shares of Deutsche Telekom fell as much as 5 percent to a 16-week low on Wednesday after Sprint abandoned deal talks, and ended 3 percent lower at 11.53 euros, wiping some 1.6 billion euros off its market value.
Sprint shares plunged 18 percent, while T-Mobile was down 8 percent.
The German company, which makes about a third of its sales and a fifth of its core profits in the United States, has tried to sell the U.S. subsidiary twice since late 2011. It reasoned that T-Mobile US, as the fourth-biggest mobile network operator, lacks critical mass to compete with leaders AT&T Inc and Verizon Communications Inc.
Deutsche Telekom, which declined to comment on Wednesday, must now decide whether to open T-Mobile US's books to French low-cost telecoms firm Iliad, which has made a $33 offer for 56.6 percent of the U.S. business. Before Sprint dropped out Deutsche Telekom told Iliad it did not want to engage in talks at that price level and Iliad was searching for partners with a view to possibly raising its bid.
A bid from Dish Network Corp may also be on the horizon.
"T-Mobile is something that we would have interest in," Dish Chairman Charlie Ergen said on a conference call Wednesday after the satellite TV provider reported its quarterly results. He added that the company's executives have yet to discuss their plans, however.
Alternatively analysts said Deutsche Telekom now could now decide to hold on to the U.S. business until the political climate turns more favourable towards market consolidation and in the meantime lobby as a standalone operator to get a reserved bloc of the best spectrum in next year's keenly awaited auction of long wave radio frequencies.
"The news (on Sprint) was a huge shock to us," said a person close to Deutsche Telekom management.
"This is the worst scenario we could think of. The company will have to look into the Iliad offer now and may even have to consider staying around longer in the U.S."
However, Andreas Mark, fund manager at Union Investment, a top 20 shareholder of Deutsche Telekom, said the failure of the prospective Sprint deal should not change the group's strategy because T-Mobile is now "well placed" to deliver strong growth.
"There is no reason to frantically look for a buyer. Plan A is normal development. Plan B would be to consolidate - and that will come eventually."
"Accepting the Iliad offer would only make sense if Deutsche Telekom was in urgent need of money or could put the money to work better elsewhere. This is not the case."
"Anything Iliad could do to improve the position of T Mobile U.S., Deutsche Telekom can do itself as well."
Iliad's shares were down 3.9 percent at 181.65 euros, reflecting investors' misgivings about its attempt to buy the much-larger T-Mobile firm and expand out of France.
Sprint and its majority owner, Japan's Softbank, wanted to buy T-Mobile to form a stronger third player to rival AT&T and Verizon. It abandoned talks on an offer of roughly $40 a share on Tuesday, citing opposition from regulators who want a four-player market. Sprint also named a new CEO to pilot a solo turnaround effort.
Although T-Mobile US's recently more aggressive market challenger strategy has helped it win customers in recent quarters, Deutsche Telekom has been concerned that its lack of low-frequency spectrum and fixed-line infrastructure is still hampering its ability to compete.
Deutsche Telekom earlier this year scrapped its 2015 free cash flow target to invest in the U.S. business, which under Chief Executive John Legere is spending heavily on its "Un-carrier" marketing campaign by offering cheaper, no-contract plans aimed at attracting subscribers away from rivals.
After years of poor performance T-Mobile US last week posted its first net profit in a year and reported the most post-paid phone subscriber additions in the industry.
"The status quo is not so bad for Deutsche Telekom," said Hannes Wittig, an analyst at JP Morgan. "The decision to exit the U.S. is a difficult one for any CEO to take, especially given T-Mobile US's growth compared to continued pressures in Europe."
A person close to the Sprint bid predicted that Deutsche Telekom is now likely to gradually sell down its remaining 66 percent stake in T-Mobile US and not participate in any share issues needed to raise capital for spectrum purchases.
One analyst estimates that T-Mobile US will need anywhere from $5 billion to $10 billion for the upcoming spectrum auction depending on how it is set up by the U.S. Federal Communications Commission.
T-Mobile and Sprint hoped to bid together in the auction but the FCC rejected the idea, saying joint bids might "have the effect of suppressing meaningful competition."
The auction would be the first opportunity in years for wireless carriers to buy low-frequency airwaves, considered the best radio spectrum for their reach. (Additional reporting by Peter Maushagen in Frankfurt, Lisa Richwine in Los Angeles, Liana Baker in New York and Leila Abboud in Paris; Writing by Leila Abboud; Editing by Tom Pfeiffer, Greg Mahlich and Richard Chang)