Warner Music chief Edgar Bronfman has hit back at Apple chief executive Steve Jobs's open letter suggesting that music companies should abandon digital copy protection. 

Bronfman used his speech at a 3GSM forum to call on Apple to open up its iTunes software to other forms of DRM.

"DRM and interoperability are not the same thing," he said. "Warner Music believes very strongly in interoperability. Consumers want it and consumers should have it."

Despite Jobs's call for free access, Bronfman insisted that all parties could agree that intellectual property deserves some measure of protection.

"But there cannot be so much protection that you create a poor consumer experience, and we need to find a better balance than exists today," he added.

In a separate conference call, Bronfman told reporters that music deserved the same protection as software, film, video games or other intellectual property.

Jobs's open letter to the industry had asked the four major players - Universal, EMI, Sony BMG and Warner Music - to remove DRM protection from the products they sell. 

However, Bronfman pointed to mobile devices as the future of the industry and praised Apple's upcoming iPhone.

"The opportunity for mobile is huge and it is remarkable that we are selling as much music as we are on mobiles given how difficult it is to access," he said.

"The average ring-tone download is two and a half minutes and takes 20 clicks. If you could make that two or three clicks, if you could make that 10 seconds, the amount of revenue that would unlock is extraordinary."

Bronfman added that the iPhone had already raised the bar of people's expectations even before it has hit the market.