This post enabled me to figure out that Google Voice doesn’t insist that a number be “reclaimed” if one tries to associated it with more than one Google Voice account. The actual restriction is on SMS handling. In my particular case, I just want the phone to ring. The trick is to register the mobile phone as a Home or Work phone with both Google Voice accounts. If no SMS message support is involved, then Google Voice won’t insist on “reclaiming” the number.