The Washington-Baltimore region has the worst cell phone service of any major city in the county, according to a new study.

The region ranked worst of the top 27 markets, with 18 problems per 100 users, according to the report from J.D. Power and Associates. However, the authors cannot explain the region's poor performance.

"To be honest, I don't exactly know [why service is poor in The District]," said Ross Gagnon, J.D. Power's manager of telecommunications.

The seven-prong report looks for static, echoes, dropped or failed calls, and untimely call or text notification every six months. The report studied more than 26,000 customers nationwide -- 813 locally -- over the last six months of 2010.

The growing popularity of smartphones and an uptick in indoor calls -- both prone to weak reception -- are to blame for a growing number of cell phone problems, the study found. In the past eight years, indoor calls, made mostly from home, increased 16 percent, as homeowners cut off their landlines.

Decade-long Verizon customer Nick Musso, 26, of D.C. said he has problems in buildings and on Metro.

"As soon as the train leaves, it drops your call," he said, noting he does not use a smartphone.

Increased texting -- up 65 percent from two years ago -- is also to blame, according to the study.

AT&T and Verizon tied for best service in the mid-Atlantic, with one fewer complaint per 100 customers than Sprint Nextel or T-mobile. Verizon swept most of the nation for best service.

Verizon smartphone customer Liz Anderson, of Columbia, said she switched from Sprint four years ago because of poor connections.

"I couldn't get reception in my office or on the street," she said.

Cincinnati and Pittsburgh scored the best, with six complaints per hundred customers.