T-Mobile USA is building up its 3G coverage, but it’s feeling the effects of intense competition. The carrier lost 77,000 customers in the third quarter, ending the quarter with 33.4 million customers.

Contract churn was 2.4 percent in the third quarter – the same as it was in the year-ago quarter but up from 2.2 percent in the second quarter. T-Mobile blamed the uptick in part to “competitive intensity, including handset innovation, and the seasonal impact from the ‘back-to-school’ window.”

In a statement, President and CEO Robert Dotson said that over six months, the carrier will have almost doubled its high-speed coverage with the goal of reaching 200 million consumers by the end of this year.

T-Mobile says its entire 3G network will be HSPA 7.2 Mbps-enabled by the end of this year. In September, T-Mobile launched a trial of HSPA+ technology with a maximum download speed of up to 21 Mbps in Philadelphia.

The carrier says 2.8 million 3G-capable converged devices (such as the T-Mobile MyTouchTM, T-Mobile G1 and the T-Mobile Dash 3G) were on its network at the end of the third quarter.

Net income for the third quarter was $417 million compared with $425 million in the second quarter and $442 million in the third quarter of 2008. ARPU was $47 in the third quarter, down from $48 in the second quarter and $52 in the year-ago quarter. Data services revenue represented 21.1 percent of blended ARPU, or $10 per customer, which was up from $8.90 per customer a year ago.

The average cost of acquiring a customer, or CPGA, was $290 in the third quarter, which was in line with third quarter of 2008.

Yesterday, the carrier said it had cleared up service problems that were interfering with calls and text messaging for about 5 percent of its customers. Outages had been reported from Atlanta to Los Angeles.