If you set up a Google Voice account and/or a VoIP provider on your OBi, it will be just like dialing on a landline service:
7, 10, or 11 digits will be US/Canada calling. It will be a free call through Google Voice and may or may not be billable through your VoIP provider or your landline depending on the plan you have with them.
011 + country code + number will be an international call and will be billed at the rate Google Voice, your VoIP provider, or your landline telephone company charges. Either your landline, Google Voice, or your VoIP provider can be set as your default provider and you can use one of the others instead by prefixing the number with **1, **2, or **8 as appropriate.