A toy which changes the characteristics of people's voices, is proving a hit with practical jokers, suspicious spouses and, more worryingly, confidence tricksters.

In the 30-odd calls Zhu Liangsheng has made in the past two days, sometimes he sounded like a man and sometimes like a woman.

"In one call to a male friend, I had my voice transformed to a middle-aged woman," he said, referring to a voice-changing gadget he bought recently.

"I pretended to be a woman complaining he had harassed my daughter.

"My friend was shocked and totally confused, it was really funny."

The device Zhu used can transform the user's voice to make it totally unrecognizable, even as far as giving voices a different gender. Most of the devices, which can be bought for around 30 yuan (US$3.75), have three to eight voice models to choose from.

"Some of my friends couldn't believe it was me even after I told them," Zhu said.

"But I was careful not to offend them and none of them were mad with me after I explained the joke."

Zhu found the gadget while shopping at an electrical appliance market.

"So far, I haven't seen any big stores selling it," Zhu said.

"But I was told by the man I bought mine from that he had sold more than 100 in a week."

The vendor, surnamed Li, said he bought the devices from Shenzhen in south China's Guangdong Province. Having become popular across southern China, they have only recently appeared in Shanghai.

The devices are easy to obtain on the Internet.A search of one of Shanghai's major auction web sites found about 100 online stores selling them.

One online vendor said the voice changer could help users avoid phone calls they didn't want to pick up.

Xu, a senior manager at a consulting firm,claims he gave himself a whole week of rest over the national holiday by doing just that.

Whenever he had a call from work, he changed his voice and told callers Xu was not available, he said.

And, according to Shanghai vendor Li, the device can be used to test the fidelity of spouses.

"If you suspect your husband or wife is having an affair, you can call them with the device and see how they react," he suggested.

But Li also warned people not to use the device to commit fraud, something that has already occurred.

Two men in Jiangsu Province were sentenced to eight and nine-and-a-half years in prison for fraud using a voice transformer.

In June, the men called a man in Gaoyou,Jiangsu Province, telling him he had won a lucky draw. In order to claim the money,they told the man he first had to pay a certain amount of tax money which they actually intended to steal.

They were able to set up the scheme by using the voice changer and appearing to be several different people.