U.S. Cellular lost 31,000 customers in the first quarter, marking the fourth sequential quarter of declines in its customer base.

The regional operator lost 9,000 net prepaid customers and 22,000 net postpaid customers as it struggled to compete with larger postpaid carriers and competitively-priced offerings in the prepaid market. 

The company’s subscriber base now stands at just over 6 million, down from about 6.15 million during the same period last year.

“It’s clear from our subscriber results that we need to increase awareness of the unique value and benefits we offer to potential customers,” U.S. Cellular President and CEO Mary Dillon said in a statement.

The company plans to accelerate its deployment of LTE, with its first markets launching in the latter part of this year. Dillon did not provide additional details about the company’s LTE deployment plans.

The company’s smartphone lineup will also get a makeover. Dillon said the company will introduce at least 13 new smartphones over the course of 2011, including some lower-priced models intended to coax feature phone users into upgrading their handsets.

Customers continued to switch to U.S. Cellular’s Belief Plans, which reward subscribers for their loyalty to the carrier. About 1.8 million new and existing customers signed up for the plans during the quarter.

The news wasn’t all bad. U.S. Cellular managed to make improvements in the company’s churn rates and postpaid ARPU. Postpaid ARPU rose to $51.21, from $50.70 last year, and postpaid churn improved to 1.37 percent from 1.41 percent.

Profits declined 28 percent despite a rise in sales as the company spent more money on marketing and handset subsidies. U.S. Cellular made $34.1 million in the first quarter on sales of $985 million, compared to profits of $47 billion on sales of $965 million last year.