Apple’s iPhone is likely to see new third-party applications soon.

Over 100,000 developers have downloaded the free software development kit (SDK) Apple (NASDAQ:AAPL) unveiled last week.

Several big name software firms issued statements supporting the SDK, which is currently available as a beta or test form. The complete version, which will include the launch of online Apps store (the only Apple-authorised distribution method for iPhone software), isn’t out till June.

Business software makers Intuit (NASDAQ: INTU) and NetSuite (NYSE: N) along with blogging tools provider Six Apart, said they planned to develop for the iPhone using the SDK. Salesforce.com (NYSE: CRM) and Epocrates (a maker of decision support tools on mobile devices for healthcare) announced their support at last week’s event.

Games companies also said to day said they are developing for the iPhone. These include; THQ Wireless, Rocket Mobile, PopCap, Electronic Arts and Sega.

The new developer announcements also follow last week’s news that high profile Silicon Valley venture firm Kleiner Perkins Caufield & Byers has launched a $100 million “iFund” dedicated to funding iPhone-related software and services.

Rick Jensen, senior vice president of Intuit’s small business group said, “The iPhone SDK gives us the tools we need to create powerful iPhone applications and is an important part of our overall mobile strategy.

“We’re excited that the iPhone expands the ways our customers can solve key financial tasks wherever they might be.”

Other developers have similar optimism that the iPhone will allow professionals to get more done on the go.

“NetSuite is excited at the opportunity to give every iPhone customer access to their critical business data anytime, anywhere,” said Luke Braud, vice president of software development at NetSuite.

Chris Alden, CEO of Six Apart, said his company is using the SDK to build on the iPhone-optimized blog service it already offers. “We’re taking it to the next level with our native iPhone application for TypePad that’s already in development,” he said.