Hi! I found this in a search while trying to solve the same problem. I believe this is an issue with Google wanting us to use hangouts as our default messaging app. Google has been very pushy these days, VERY pushy.
Were you ever able to find a satisfactory response to your question? Even better, were you able to find an app that will integrate phone, contacts, sms, etc.? Seems so basic and yet so impossible with the native 1+1 apps. Thanks
Pam