Additional Personal Income

[cidz0r]

I am currently in the US on a TN Visa. I have been writing several iPhone Applications on my spare time, but I am not sure how to release them. If I register with the iTunes App store under an individual license, and sell my Apps, am I going to get myself into trouble for performing work without a Visa? I know I heard someone mention somewhere that there's a key distinction if it is a Job or not, and if it's not a Job that you are taking it's okay. Does anyone know where I could find more information on this distinction?

Thanks in advance!