After a day or two of spotty outbound service at the house on two different Project Fi accounts, using both my Nexus 6 as well as my Nexus 6P, so I decided to reach out to support. After some troubleshooting we were able to determine that it was a T-Mobile specific issue that was effecting the ability to make outbound calls. Forcing the phone onto Sprint, US Cellular, or just using WiFi calling was flawless. At the end of the day it just a local tower issue as driving to a different location worked fine.
At the end of the call I compiled the notes I had taken during the call and asked the support person to fill in the blanks. I am sure there are more codes but here are the ones we used, just punch these into your dialer app on any Project Fi phone and off you go…
*#*#344636#*#* – Code to determine current network.
*#*#34777#*#* – Code to switch over to Sprint’s network.
*#*#34866#*#* – Code to switch over to Tmobile’s network.
*#*#34872#*#* – Code to switch over to U.S. Cellular’s network.
*#*#342886#*#* – Code to go to Auto (auto switching enabled).
The support rep mentioned that after 2 hours or so that the phone should default back to auto mode.
Hope this helps you in your travels or just as a work around for spotty/temp service issues.