iPhone 2G (oldest iPhone) supports only iOS 3.1.3 (max).
Openmaps 3.6 requires iOS 4.
Please make a 3.1.3 version available seperately or restore compatibility in the near future.
The old iPhone is the only one available for about $200 (used) and with open software like BTstackGPS supports bluetooth gps devices too. I just recently bought one and this app.