How will you know if a member has enabled this feature? Look for the "Call me at Ccube" button.
To launch this feature, CCube offers a free, 60-minutes-a-month pricing option. $7.00 gets users 250 minutes a month, and $20.00 allows for 1,000 minutes a month.
I think there will be some takers for this service, but the real issue will be to break the IM and texting model in which so many members of this universe are tethered to.