Yes, I posted yesterday, that this was the bug that was keeping my integration from working. It's actually listed in the Known Issues, but I didn't notice it until yesterday. Sorry for cross-posting, but here are the details I gave in another thread to a user asking where to find this:
I don't know why it matters if this feature is enabled or disabled, but apparently it does matter. It's mentioned here:
is a Sprint feature intended to help you block unwanted callers from
calling your Sprint phone. It is buried down in their customer web
portal, under the My Preferences tab. Scroll down to "Limits and
Permissions", then click on "Block Voice". Select the device (your cell
phone) if you have more than one on your account, then disable the
phone number blocking function if it's currently enabled.
Per the Google Voice FAQs, you can accomplish the same type of blocking from GV itself, if you need it.