I needed to seasonally park one of my phones and found out something interesting. If you integrate your Sprint number and Google Voice, thinking that your Sprint number IS your Google Voice number ... it isn't.

Your number *doesn't* become a real Google Voice number. It is just a cosmetic layer that allows you to use it in a similar way. If you park your number ( like I did ) or drop your Sprint account, then you will need to setup a new Google voice number because the Sprint number gets pulled out of Google integration automatically.

The only way I can think of working around this is to pay to migrate your Sprint number to Google Voice and then get a new number for your phone.The same thing as what you would have to do with any other cell provider.