DENVER -- More than half a million Colorado phone numbers have been added to a list for people who don't want calls from telemarketers.

Coloradans had signed up 501,975 numbers for the no-call list as of midday Monday, said Don Knox, spokesman for Colorado No-Call.

The Legislature established the list last year. Enforcement begins July 1.

Telemarketers must buy the list within 20 days of each quarterly update. Violators with three or more complaints in a month can be prosecuted and fined $2,000 per violation.

This is the last week to sign up for the program if you want to be on the first list that telemarketers must buy. Those signing up after May 31 will not have their number provided to telemarketers until Oct. 1.

The toll-free number is (888) 249-9097, or it's on the Internet at www.coloradonocall.com.

Since the list opened May 8, the program has registered about 25,100 numbers a day on average, Knox said.

"Demand has been terrific, and we expect another heavy week as the deadline approaches," Knox said.

More than 300,000 residents who added their names to a no-call list managed by the Big Horn Center in the past 17 months will be contacted via e-mail or telephone to confirm their registration. About 313,000 people registered with the Big Horn Center, a nonprofit advocacy group that lobbied for passage of the bill.

Being on the list won't make all unsolicited calls a violation. For instance, charitable groups and companies that already do business with residents, such as the phone company, could still call.