Tough new rules for TV quiz shows and channels have been introduced by the premium rate phones watchdog.
Viewers must be told how many other people are trying to take part
Viewers must now be warned if they spend more than £10 on phone calls and must be told how many other people are calling to try to take part.
The new Icstis rules are designed to rebuild the trust of viewers after a series of complaints about the use of premium-rate phone lines on TV.
The shake-up follows a highly critical report by MPs on the issue.
MPs were told of viewers who had spent thousands of pounds trying to get through to answer questions, including one person who had made 60 calls in eight minutes.
They also heard claims of shabby practices by producers to stop viewers being put through.
The radical new rules could dissuade some people from calling.
On screen, viewers must be shown the number of people calling to take part.
And the price of calls must be read out by the presenter or a voiceover every 10 minutes.
Viewers must be warned every time they spend £10 on calls in a day.
Companies which don't comply could face heavy fines.
Last week, the company behind telephone quizzes on breakfast TV programme GMTV admitted "certain irregularities" and apologised to viewers after the BBC's Panorama programme found some quiz entrants had no chance of winning.
That followed a long line of complaints surrounding the use of premium-rate phone lines by TV companies.
BBC One's Blue Peter recently apologised for featuring a fake contestant after a technical glitch hit a phone-in competition.