Mobile executives at a Silicon Valley roundtable discussion threw down the gauntlet to Symbian, Android and other software platforms to match the impact of the iPhone.

Talking only about two weeks after the introduction of Apple's iPhone 3G and the App Store, where third-party software for it is offered, heads of some software companies reported huge numbers of downloads and proclaimed a new day on the mobile Internet. The jury is still out on whether the open-source phone platforms coming from Google and the Symbian Foundation will be able to match Apple's success, according to the panelists at the TechCrunch Mobile Web Wars event in Menlo Park, California, on Friday afternoon.

For example, Pandora Media began offering its Internet radio application for most other mobile platforms, through carriers, about 18 months ago, Pandora CTO Tom Conrad said. That resulted in about 12,000 paid monthly subscriptions to the service, he said.

"In six days, we had 350,000 installs on the iPhone," Conrad said. A key factor was that the App Store let the company give away its client and support its service through ads. On other devices, Pandora has had to use carriers' monthly subscription model, he said.

Nearly 1 million Facebook users have downloaded the social-networking company's application to their iPhones, according to Jed Stremel, director of mobile at Facebook. And Loopt, a location-based social-networking startup, reached 100,000 iPhone downloads only about a week after the App Store opened. The average iPhone user also is 47 times as active on Loopt as those on other types of phones, said Loopt cofounder and CEO Sam Altman.

"You can make such a beautiful app, and it's so nice to use, so quickly, on the iPhone," Altman said.

Some panelists balked at the iPhone-centric focus of the discussion, saying the importance of the device is exaggerated in Silicon Valley.

"The statement that somehow the Web has not been mobile until the iPhone showed up is absurd," said David Rivas, vice president of S60 software technology management at Nokia. He also said the company's current S60 software platform can do most of what the iPhone can.

Tapulous, a vendor of iPhone applications including the Tap Tap Revolution game and a Twitter client called Twinkle, is already beginning to exhaust the relatively small user base of the iPhone, said Bart Decrem, CEO of Tapulous.

"I wish there was another place where I could offer this experience," Decrem said.

"I've got a couple hundred million devices for you," Rivas said.

"Oh, yeah, if you could give me a developer environment ... and a delivery channel," Decrem shot back.

Even Rivas acknowledged that Apple has broken new ground by establishing a new kind of relationship with carriers, in which it can run its own online software store. Whatever existed before in mobile data, that change has made venture capitalists take notice, said David Hornick, a partner at August Capital.

"Why are venture investors excited about mobile applications now, in a way they weren't before? It's because before, there was no good way to get them on the phone. And why is the iPhone an incredibly compelling platform? Because, in a weekend, thousands and thousands of applications were distributed," Hornick said.

Most of the software CEOs expressed interest in developing for Android but are wary that it will go the way of Java, with too many different versions to adapt to.

"I need Android like I need a hole in the head," said Pandora's Conrad, picturing it as "another OS platform that sits on top of buggy firmware, with devices with hundreds of manufacturers, with different characteristics."

Loopt's Altman said one valuable feature of Android is the ability to have tasks run in the background. He praised the openness of Android, which will allow Loopt to create a contact list with live location information, something that would not be possible on the closed iPhone environment. Whether Android's open-source model will work out well is uncertain, but it should become more clear pretty quickly, Altman said.

"I would guess a month post-launch of Android, you will have a feel of how much people are going to follow the spirit of one stack that works with everything," Altman said.

As for Symbian, Nokia's Rivas emphasized that the transition to the open-source platform won't happen overnight. But he acknowledged that there is another major step Nokia has to take to generate interest at the software epicenter of Silicon Valley.

"Once I have a collection of phones here in the U.S. market that you guys are willing to hit, suddenly the whole value proposition changes for you," Rivas said.