UPDATE 3-Sprint shares soar on T-Mobile USA tie-up talk

* T-Mobile USA would jump to No. 2 U.S. spot from No. 4

* Analysts warn of tech obstacles, regulatory scrutiny

* Analysts say DT would need financing to buy Sprint

* Deal comes amid wave of M&A in competitive mobile market

* Sprint stock up 14 pct, Deutsche Telekom down 1.15 pct (Adds analyst comment, share price update)

By Nichola Leske and Sinead Carew

FRANKFURT/NEW YORK, Sept 14 (Reuters) - Sprint Nextel Corp (S.N) shares jumped 14 percent on speculation that the No. 3 U.S. mobile service might be bought by Deutsche Telekom (DTEGn.DE) even as many analysts said such a deal would be very difficult to pull off.

Together, Sprint and Deutsche Telekom's T-Mobile USA would vault to second place in the U.S. mobile market, where they are each having trouble competing against each other as well as market leader Verizon Wireless and No. 2 AT&T Inc (T.N).

But investors were concerned that a Sprint deal would be too costly for Deutsche Telekom and too tough to integrate given their different network technologies. Sprint has a market value of $12 billion and more than $19 billion in liabilities.

Shares of DT, which have a market value of 41 billion euros ($60 billion), closed down 1.15 percent at 9.425 euros and were the sixth biggest loser on Germany's DAX index .GDAXI.

"Despite the potential benefits of a merger we believe combination would also present several challenges," said Piper Jaffray analyst Chris Larsen. "There's no easy deal or no easy road map to a single technology, which is where your synergies come from," he said.

Such a merger would also face a tough review by U.S. antitrust regulators, analysts and regulatory experts said.

Deutsche Telekom and Sprint declined to comment on the merger speculation, which was first reported in Britain's Sunday Telegraph. CNBC reported that Sprint was not aware of any overtures from Deutsche Telekom, citing sources.

Sprint shares rose 50 cents at $4.27 in afternoon trade.

"We believe if Sprint were to be acquired, the board would require a premium valuation in the neighborhood of five (times estimated) 2010 EBITDA, which would equate to roughly $5.50 (per) share," said Michael Nelson of Soleil/Nelson Alpha research. He said Sprint shares currently trade at about 4.2 times estimated 2010 EBITDA.

Heino Ruland of Ruland Research said Deutsche Telekom would have to raise money for a Sprint bid and worried about the "time span needed to return the U.S. peer to profitability." Deutsche Telekom had 5.8 billion euros in cash and cash equivalents as of June 30, according to Reuters data.