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I use Google Voice as my primary phone number. At home, I have an Obihai analog telephone adapter and it works flawlessly. At work, I have Google voice ring my desktop phone, and that works great too.
As for my cell phone, Google likes to keep Hangouts and Hangouts Dialer on the cutting edge, so if you use it to place or receive voice calls, be prepared for the occasional broken update. It is good to keep FreedomPop Messaging around as a backup, because you will need it for voice calls when Hangouts isn't working.
As soon as I got my phone from FreedomPop (Nexus 5), I wiped it and put on the stock/generic ROM. I never once used the FreedomPop ROM they had loaded onto it.
You can then download the FreedomPop Messaging app to have it activate service, view account info, get calls and text working, etc.
For iOS APN, go to https://www.freedompop.com/iosapn and select United States and US LTE SIM and download the profile.
For app download goto https://www.freedompop.com/appdownload
In my LG G4, I use this app - https://play.google.com/store/apps/details?id=com.freedompop.phone&hl=en
Appears now they've brought the FreedomPop Messaging Phone/SIM app back to Google Play.