"We are still relatively small ... I expect the volumes on Windows Phone to really ramp quickly," Ballmer said, as reported by the Reuters news service. Ballmer made the remarks at a Windows 8 launch event in Tel Aviv.
"With the work we have done with Nokia, HTC, Samsung and others ... there is now an opportunity to create really a strong third participant in the smartphone market," Ballmer said.
The optimism from Ballmer is to be expected, analysts noted.
Ramon Llamas, an analyst at IDC, said his view of the Windows Phone operating system is more conservative.
"Windows Phone 8 is a great platform, well differentiated, well designed and a lot of fun to use," he said. "I just have reservations as to how well the messaging around WP8 can be carried out and if it's enough to convince end users to make the switch, especially if they're already into Android and iOS."
Both Android and Apple's iOS have a big head start on Windows Phone, as well as more apps, analysts noted.
IDC said in an updated forecast in October that Windows Phone will grow from 3 percent of the global smartphone market in 2012 to 14.2 percent in 2016. That growth means Windows Phone would rank third in 2016, while iPhone would be second with 21.2 percent and Android would be at the top with 58.6 percent.
Gartner recently said Windows Phone would reach 13 percent of the smartphone market in 2016, up from 2.5 percent in 2012. The market research firm also ranked Windows Phone third in 2016.
IDC expects Windows Phone to jump to third place, with 6.6 percent market share, as early as 2013, in part due to the decline of BlackBerry, with 4.7 percent market share.
Llamas agreed that third place "is a big deal" partly because it means that carriers will stock Windows Phone 8 devices on their shelves, while there is less room for less popular phones. "There's only so much shelf space," Llamas said.
Microsoft also could benefit if the company convinces customers that Windows Phone 8 fits into an ecosystem with other Windows 8 devices, including tablets, he added.
Llamas said Microsoft has to show the benefit of its mobile operating system, including its "live tiles" on the interface, as Ballmer did in an online ad for Windows Phone 8 unveiled last week.
What Microsoft needs to do less of is produce advertising like the TV commercial for the Surface RT tablet, Llamas said. That ad is flashy and features dancers clicking tablets together with their covers and clicking open Surface kickstands in rhythm.
"It's nothing about the actual interface," Llamas said. "It leaves me asking, 'What's so great about this?' "