A man randomly sent around 32,000 sexually explicit mobile phone messages - many to children, Caernarfon Crown court has heard.
Royce Roberts, 42,from Caernarfon, made the calls sending pornographic images at a cost to him of ?25,000.
The offences began after Roberts looked at chatrooms following the breakdown of a relationship, the court heard.
He admitted 15 offences of causing children to watch an indecent image. He will be sentenced on 26 June.
Roberts, a painter and decorator, also admitted four offences of possessing indecent images of a child and another charge of causing a public nuisance by making unsolicited, voice text and video calls.
Prosecuting Simon Medland said Roberts sent the pornographic images to randomly selected numbers using the latest generation of mobile phones.
"The defendant would make random calls, and when they were answered, he'd show explicit images and send explicit texts."
"He would bribe his child victims, saying he would buy top-ups for their mobiles if they showed him their private parts and took a look at his.
"With one 14-year-old girl he indulged in an extensive course of calls, passing himself off as a 17-year-old boy called Kevin. He received explicit images of her and sent explicit images of himself to her."
Mr Medland added: "One child victim said she thought the images were disgusting and dirty, and she didn't think they should be allowed to be sent.
"Another nine-year-old boy received obscene pictures and said the whole thing made him feel sick."
In all 1,500 messages were sent to children.
The calls or attempted calls were made over an eight-month period last year at the rate of about 1,000 a week. Roberts used seven phones to make the calls.
The court was told that the case arose after complaints were made to police in Strathclyde. There were also a spate of calls in Essex, as well as in Chester, Shrewsbury and Birmingham.
Defending, Daniel Travers, said Roberts "deeply regrets his actions", on which he had spent about ?25,000.
The offences started after Roberts begain looking at internet chatrooms after the breakdown of a relationship, said Mr Travers.
"He accepts what he was doing was wrong, and having made contact with children he regrets not breaking it off."
"He accepts he caused a risk to children, and that this behaviour cannot be tolerated."