T-Mobile USA today gave its parent company, Deutsche Telekom, something to cheer about, announcing that it added just over 100,000 subscribers in the third quarter. That’s up from a loss in net subscribers in the second quarter.

The subsidiary of Deutsch Telekom reported a year-over-year drop in service revenues of $4.71 billion compared to $4.73 billion in the third quarter of 2009.

Additionally, the number of customers using smartphones at T-Mobile continued to increase significantly during the quarter, driving blended data ARPU, which includes an average of postpaid and prepaid customers, of $12.40 in the third quarter of 2010, up from $11.60 in the second quarter of 2010 and $10 in the third quarter of 2009

T-Mobile said that 7.2 million customers are using smartphones as of the third quarter of 2010, compared with 6.5 million as of the second quarter of 2010 and 2.8 million as of the third quarter of 2009

T-Mobile’s earnings are announced in conjunction with Deutsche Telekom’s, which expressed its satisfaction at seeing its struggling American counter-part doing well.

“I am very pleased with the development of blended data ARPU. Along with the growing number of smartphones, this demonstrates the potential of mobile broadband data growth in the U.S. market and for T-Mobile USA in particular,” said Deutsche Telekom CEO René Obermann in a statement.

T-Mobile has the pipes to serve up that data now. The company’s HSPA+ network, which it calls 4G because it matches or betters speeds seen on competing WiMAX networks, has been rolled out in 75 major metropolitan areas across the country. The company said it is on track to reach 100 major metropolitan areas and 200 million people in the U.S. by the end of this year.