There isn't an exact substitute for that method as of now. The old Google Voice Chrome Browser extension has a "turn phone numbers into clickable links" feature. It also has a "call with" feature similar to the red CALL button in GV. As of tonight, it still shows Chat as a call-with target. I dunno when they will pull that one too, but my guess is fairly soon. The devs are aware of the need for Hangouts to perform a function like that, and they're looking into it, but no ETA.
Your options (aside from what I already mentioned above), are to use a non-GV telephone number as your call-with phone number, or, if you depend on this for your living, like an inside salesman or broker, or other person who uses a CRM software package, to use a new add-on that provides true CTI (Computer-Telephone Integration) between Hangouts and a CRM product. Big bucks, but instant ROI. There is no freebie/cheapskate alternative software option.
Way down the road, would just be idle speculation, that Hangouts will gradually support more of these VoIP telephony functions natively.
Last comment here, and then I need to move on: rest assured that several GV team members at Google are OBi fans and they are now avid OBi users, too. They'll be making ongoing changes to GV and Hangouts with an eye to ensuring that GV support for OBi devices continues, with the appropriate continuation of access to the GV infrastructure by OBi users. None of the Chat "sunset" actions happening now will shut down nor cripple GV use on OBi products.