Japan's third-largest mobile carrier Softbank on Friday unveiled a lower monthly fee for the new iPhone than bigger rival KDDI, as competition for smartphone users heats up among the nation's mobile firms.

Softbank's exclusive grip on the iPhone in Japan ended with KDDI having struck a deal to also sell the popular device. Both firms began taking advance orders Friday ahead of the iPhone 4S's October 14 launch.

Softbank had enjoyed a monopoly on the iPhone as Apple's only carrier in Japan since the phone was released in the country in 2008. It also carries the iPad tablet computer.

On Friday, the company unveiled a fixed monthly data communication fee of 4,410 yen ($58) for the iPhone 4S, undercutting the 4,980 yen announced earlier by rival KDDI.

Softbank announced the plan at a hurriedly arranged press conference less than four hours before the two firms began taking advance orders, helping its shares close up 6.50 percent at 2,456 yen on the Tokyo Stock Exchange.

KDDI shares closed up 1.42 percent at 568,000 yen.

Competition in Japan's smartphone market is to heat up with Softbank and KDDI battling to win iPhone users on top of challenges from other phones such as the Galaxy made by South Korea's Samsung, offered by top carrier NTT DoCoMo.

The iPhone 4S features a speedier processor, a built-in "personal assistant" that responds to voice commands and a more powerful camera.

Its unveiling on Tuesday was met with disappointment that it was not the revamped next-generation iPhone that many Apple fans had hoped for.

However, some analysts say consumer demand could be shaped by an outpouring of emotion surrounding this week's death of Apple co-founder Steve Jobs.

Yusuke Tsunoda, telecom analyst at Tokai Tokyo Research, said "it is difficult to see a clear positive" for both Softbank and KDDI.

"It is surely negative for Softbank that its iPhone monopoly has broken down with users now having another option," he said.

Friday's jump in Softbank shares "does not necessarily determine the future direction of the stock," he said, arguing Softbank's fees were not low enough to sway those loyal to KDDI's 'au' network.

Offering the popular smartphone will be sure to "benefit 'au' as the iPhone helped Softbank snatch customers in the past," Tsunoda said.

"But it is still uncertain how many new subscribers KDDI can win," he said.

"I do not expect the benefit would show in (sales) figures soon as many consumers are likely to take a wait-and-see stance" before they decide which company they will choose, he said.