Of course. That is exactly how Google Voice works.
Log into your Google Voice account from a laptop or desktop computer, not from a mobile browser, and go here:
https://www.google.com/voice#phonesAdd your VoIP number as a forwarding phone number, and go through the verification process. Change any settings you wish for the number while you are here. Also, take a look at that list of forwarding phones, and remove the check mark from, and delete any numbers you no longer control. Otherwise, when those numbers are reissued, the new owner will get your calls and texts.
Go back to the OBiTALK portal. Adjust your settings so that you do receive inbound calls on your
voip.ms number, and do not receive them on your GV service provider slot. If you configure GV as SP1, and GV as SP2, then by default, outbound calls will use GV. There are "fancier" ways to control this behavior, but I'll leave that discussion to guys like azrobert, if necessary.