Mobile phone users commonly experience four common problems concerning technical glitches and unwanted intrusions, a U.S. poll indicated. The Pew Research Center\'s Internet and American Life Project said 72 percent of cellphone owners asked reporting dropped calls at least occasionally and 32 percent say they encounter this problem at least a few times a week or more frequently than that. In the poll, 68 percent of respondents said they receive unwanted sales or marketing calls at one time or another, with 25 percent seeing them at least a few times a week or more frequently. Of those with phones that have texting capabilities, 69 percent told pollsters they get unwanted spam or text messages. Finally, of those who use their phones to go online -- to browse the Internet, exchange e-mail or download apps -- 77 percent of those asked complained of slow download speeds that interfere with the process. Telephone interviews were conducted by Princeton Survey Research Associates International from March 15-April 3, among a sample of 2,254 adults, age 18 and older. The sampling error was 2.4 percentage points.