Sony Ericsson, the world's fourth-largest handset maker, plans to launch an ultra-slim, high-end Walkman camera phone in early 2007 to take on Motorola's blockbuster RAZR, according to Reuters. The RAZR's runaway success spurred Samsung to launch a copycat line of slim phones in the summer, which helped boost the South Korean firm's handset sales and margins in the third quarter.

Sony Ericsson will unveil its rival to the RAZR, dubbed "Ai," in March next year, the source said.

Inspired by Japanese tennis player Ai Sugiyama, the sleek candy bar-shaped phone will measure 9.4 millimeters in thickness, slimmer than the RAZR's 14 millimeters. It is expected to be launched in black and silver.

Unconfirmed rumors about "Ai" and other new models from Sony Ericsson have also been circulating in various online blogs.

Sony Ericsson jumped back into fourth position -- from fifth place -- for the first time in two years in the second quarter, overtaking LG, according to research firm Strategy Analytics.

It also became the world's most profitable cellphone maker in the third quarter, pipping industry leader, Finland's Nokia, which held the title for many years, according to a Reuters survey.

Sony Ericsson, which suffered heavy losses four years ago, has benefited from strong demand for its high-end Walkman music and Cybershot digital camera phones.