I've had an iCard for four years. I've travelled all around with it to National races and while only maybe 1/2 the races actually use the transmitting equipment, at those 50%, the system has only worked well enough to be helpful maybe 30% of the time. (For those doing the math, that means it's only been useful at 15% of my races). It's useful at 0% of my regional races, since my region doesn't use the system.
I understand, as Speed Raycer said, that the problem is fundamentally with the software that transmits the signal, not with the handheld device -- although the limitations of a Gameboy platform are also part of the problem with the usability.
Bottom line -- if someone's thinking about this ... I wouldn't bother.
And for the original poster -- it's understandable if a region doesn't want to get into it ... it's just going to lead to complaints. The concept is better than the implementation.
Now, if there were a next-generation iCard, with truly easy-to-use set-it-and-forget-it transmitting software, and a more intuitive user interface on the handheld device ... that could actually deliver on the concept ... now, that would be something.