All those platforms still have their problems with sound and the iPhone 4 has a hard time filling all its pixels, but the games remain to be playable even on the 1st gen iPod Touch. You can read a bit more about Impact on mobile platforms in the documentation.
Even with iOS support, it might come as a shock to some of you that I am selling Impact, rather than releasing it for free. I love free and open source software and I've been contributing stuff for quite some time now. I had a hard time thinking about whether to release my Game Engine for free. The reason I decided to charge for Impact is a) it is easily the biggest thing I've ever made and I'd love to continue working on it full time, and b) I believe it is worth the money.
Read more: PhobosLab