One of the highlights of Monday’s Worldwide Developers Conference (WWDC) keynote was when Apple’s Scott Forstall called Line 6 and Planet Waves to the stage for a demo.

There was probably nobody in the audience more excited than me when Line 6 co-founder Marcus Ryle took the stage. Accompanied by a guitar player and a helper turning the dials, Ryle debuted a new app that allows you to control your guitar amp and guitar using the iPhone.

The app works like this: the iPhone connects to a small hardware box with an output to your Line 6 Vetta II amp. When the iPhone app is running, you can scroll through the presets on the amp, change settings, load new presets or save presets to your iPhone.

In fact, you can load all of your favorite presets into your iPhone, go to a gig or rehearsal and load everything in to someone else’s Vetta II amp. Changing the amp is only one aspect of what the software can do.

You can also change the settings on Line 6’s Variax guitar. If you’ve ever used one of the company’s guitars you know how versatile an instrument it is. You can change tunings, body, pickups and many other options with the touch of a button–now that button is one the iPhone.

“It was a natural for us,” Marcus Ryle, co-founder of Line 6, told The Loop, after finishing his demo. “The iPhone is such an incredibly powerful platform, it just seemed like a great opportunity for musicians.”

It makes sense for Line 6 to be the first to offer a app and a device like this–they are the leader in amp modeling technology for digital musicians. But was developing for the iPhone more difficult than making a Mac application–not according to Ryle.

“Development went well,” said Ryle. “We only started a short time ago, but with the tools that Apple provides for the iPhone it went very well.”

Line 6 isn’t doing the development of the app and hardware alone. In fact, a lot of the credit goes to Planet Waves, a music accessory company that already has a couple of iPhone apps under its belt: Chord Master and Scale Wizard.

Planet Waves is a D’Addario company. Any guitar player will immediately recognize that name as being one of the premier brands in the music industry, but usually in hardware, not software.

“We weren’t software guys until the iPhone came out,” said Jim D’Addario chairman & CEO of D’Addario. “Now we have an entire development team.”

Both D’Addario and Ryle commented on how making this app has lead to other ideas, so it should be interesting to see what the companies can do together in the future. Whatever it is, you can be sure it will be great for musicians.