T-Mobile USA plans next month to launch two smartphones that double the speed of its wireless data service in the hope of attracting new customers to the No. 4 U.S. mobile provider.

The devices -- the Galaxy S II from Samsung Electronics Co and the Amaze 4G from HTC Corp --- will be the first phones to support T-Mobile's latest network upgrade which roughly doubles the data download speed for services such as streaming video or mobile Web surfing.

T-Mobile USA, which is hoping to win a battle with the U.S. government to gain approval to be bought by AT&T Inc, is looking for any selling points it can get over its rivals as it has lost ground to both bigger and smaller competitors.

In comparison to its current phones, which have data speeds of 3 to 4 megabits per second, the latest devices will download data at a rate of 8 megabits per second, T-Mobile USA marketing executive Andrew Sherrard told Reuters.

It's a really a nice step change, said Sherrard, who added that the speed boost would help meet demand for services such as streaming video, which has been rising sharply.

According to Sherrard, about 75 percent of the phones the company has sold this year have been smartphones. He also noted that usage of its data services have been doubling every six months and that half T-Mobile USA's data traffic is video.

Sherrard said T-Mobile was not able to get an agreement from Apple Inc to add the next version of its popular iPhone to its product line up.

T-Mobile USA's bigger rival Sprint Nextel is expected by many analysts to start selling Apple phones.

But Sherrard said Samsung and HTC devices would make up for the lack of an iPhone.

We're very confident we've a competitive line-up, he said. However, the phones are a little more pricey than most U.S. smartphones, which typically cost around $200 or less.

The HTC Amaze will cost $259.99 after a $50 mail-in rebate for customers who sign a two-year contract while the Samsung Galaxy S II will cost $229.99 after the same rebate and with the same conditions. The phones will be in stores October 12.

(Reporting by Sinead Carew; Editing by Richard Chang)

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