1. Rather than having to import and maintain a separate set of Contacts use the Android Contacts directly.
2. Register the OBi App as a dialer so when calling from the regular contacts or a direct dial short cut the OBi dialer is a choice.
If you get a one week free trial of Line2 and get the Android app it will demonstrate what can be done here. (Your VOIP is much better than Line2, so I don't recommend it as an alternative.)