From the Mobile In product FAQ:

What Apple® devices are compatible with Mobile In and Mobile POD app?

Mobile In and Mobile POD app are compatible with iPhone® 4, iPad® 2 and iPad®.

didn't notice this detail... slipped under the radar...

bummer i have a 3rd gen touch that i was hoping to use it with... i have the ipad 1 as well so that's something if i can wrestle it away from the rest of the family

I just got around to plugging in the Mobile In I got for Christmas.  What a pleasant (sarcasm) suprise to find out it doesn't work with the IPod Touch.  I wouldn't be so angry if this was the norm, but it isn't.  I've tried two of your competitors guitar interfaces and they both worked fine on my IPod Touch.  I've got 3 folders of guitar related apps that all work fine as well.  Compatibility isn't typically an issue that Touch owners worry about, especially in a product unrelated to phone usage.

I realize that Line6 has covered themselves by not mentioning the Touch in their compatibility documents.  But why not just say 'DOES NOT WORK WITH THE IPOD TOUCH'?

Hi all --

If I could just jump in here, I'm the product manager for Line 6 mobile products, so maybe I can shed a little light on the problem.  We're very sorry to disappoint iPod touch owners interested in Mobile In, but unfortunately this is out of Line 6's control. 

First off, there are no digital audio interfaces that work with all models of iPod, iPhone, and iPad, because different Apple models support different I/O technologies. So before you buy, you have to be sure the interface you want will work with your particular model.  That's just how the iOS accessories world works.  We take a lot of care to clearly indicate which iDevice models each of our mobile products works with, in fact we proudly display the Apple 'Made for iPhone - iPad' logo (and actually we thought that was pretty clear at the time). 

Second, Mobile In is a digital audio device with an input, and no output.  It turns out that none of the iPod touch models support the use of such interfaces, including not just the Line 6 Mobile In, but also the Apogee Jam and the Griffin GuitarConnect Pro.  (You can verify lack of iPod touch support over at their websites.)  So it's not just us.

Third, you folks are absolutely correct in saying that there are a number of other interfaces that do work with iPod touch.  Just keep in mind that they're all either analog inputs which have much lower quality, or else digital interfaces that include both audio in and audio out, which are more expensive products.  So there's nothing directly comparable to Mobile In that does work with iPod touch.

Again: We're really sorry there were some misinderstandings.  We would definitely make Mobile In support iPod touch, if only we could.  While we can't specifically comment on future products, please know we're very aware that a lot of iPod touch owners are interested in POD processing.  Please don't hesitate to let me know if you have any other questions about any of this.

     -- Chris Grigg

            Mobile Products Manager, Line 6