One more tidbit worth pulling out from today’s WWDCannouncements: Netflix will bring a streaming video app to Apple’s iPhone and iPod touch this summer. The company was quick to clarify two important points right out of the gate: The app is free, and it works over AT&T’s mobile 3G network, not just WiFi.

That last point is a small surprise, given that AT&T just discontinued its unlimited 3G data plan for new customers. Existing iPhone and iPad customers can keep their old arrangements, but anyone who’s signing a fresh contract will be limited to either 200 MB of 2 GB per month, depending on the plan.

If you’re planning on doing a lot of 3G Netflix streaming, you’ll want to stay on that unlimited plan since videos use up a lot of bandwidth.

Netflix CEO Reed Hastings announced the app on stage Apple’s WWDC conference alongside the new iPhone 4, but he wasn’t on stage long enough to go into detail about the app’s features. He did say that Netflix for iPhone will pick up where you left off in movies or shows you’ve already started watching — even on other devices. Also, the app uses “adaptive bitrate technology” to maintain its connection when you move between networks.

This app already seemed like a sure thing months ago when Netflix sent out a customer survey gauging interest in an iPhone or iPod touch version some time before Netflix for iPad launched

Netflix released an app for Apple’s new iPad, allowing subscribers who bought the device on launch day to access the service’s vast library of streaming films and television. The iPad won’t be stealing all of the thunder from the already-popular iPhone and iPod touch, however; a Netflix Watch Instantly app is in the works for those devices, too.

Netflix made that clear in a very brief blog post today:

Steve Swasey, VP of Corporate Communications, here. Terrific response to our news today about Netflix on the iPad. For those of you asking whether Netflix will be on the iPhone and iPod Touch: We wouldn’t invite you to dinner without planning to serve dessert. In other words, we’re working on it so stay tuned.

We already knew that a Netflix app for the iPhone and iPod touch was a possibility because Netflix has been asking users for their opinions on a hypothetical iPhone/iPod touch app in online surveys. Given that an iPad app has already been released and that the iPad and the iPhone are very similar platforms, you can understand why we’re not surprised.

This is just another step in a long march for Netflix. The service started out mailing DVDs to customers, but it has signed numerous film and TV studios to provide content for its Watch Instantly streaming service, which is now the main draw for many tech-savvy folks. More recently, video game consoles like the Nintendo Wii, Xbox 360 and PlayStation 3 have been updated with Netflix streaming capability.

Plans start at $8.99 per month. Available films and shows include 30 Rock, Weeds, King of the Hill, 24, Julie and Julia, The Proposal, Angels & Demons, The Sixth Sense and numerous others.