Short answer: yes.
Longer answer: The OBi device is just acting as one of your Google Voice account's forwarding destinations. In this case, it's the "Google Chat" destination. Your Google Voice account will still operate exactly as before, with all the same features. In addition to your cell phone, you can add up to five more forwarding phones on the GV Settings page, and you can decide which ones ring on inbound calls. Outbound calls made from the phone attached to your OBi box will show your GV phone number as the caller ID.
Disclaimer: I don't recommend GV as a business telephone service. There is no direct customer support from Google, and when, not if, something occasionally goes wrong, any small cost savings you may get from using GV will be offset by loss of business or bad reviews, when your clients can't reach you.