The hardware accessory is set to ship on April 29 and it will work with the touch, iPhone, and iPad with iOS 3.1.3 and higher. You can pre-order the hardware accessory for the device right now.
While not exactly cheap, the $297.77 you pay for the iMSO-104 is cheaper than spending over a $1,000 on a new oscilloscope (assuming you already own an iPad).
The iMSO-104 and iPad would also be much lighter and more portable than a regular oscilloscope. It is sold out due to popular demand but the next batch of devices will be shipped out on May 20.