Answers
Reunion for iPhone version 1.0.2 is fully compatible with iPhone OS 3.0
Reunion for iPhone version 1.0 and 1.0.1 are not fully compatible with iPhone OS 3.0 and may crash. If you have either of these older versions, the latest version is available as a free update.
To download this new update directly to your device, tap the "App Store" icon on your iPhone and then tap "Updates" and finally tap "Update All."
Or, if your device is connected to your Mac via USB, you can open iTunes, click "Applications" in the "LIBRARY" list, click "x updates available," and then click "Download all free updates."