Does it work with iOS4?

I downloaded and installed the free app on my iPhone 3G running iOS4. It doesnt work, always displaying an altitude of 0 and "GPS NOT READY" in red. I waited patiently for a few minutes to give the app some time -- nothing. My iPhones GPS is working just fine through Maps. If I click on the "i" it gives me info on the paid version of the app. Am I missing something? Other than that, it looks good...

hbobn about Digital Altimeter FREE