I just purchased an unlocked GSM Nexus 6 phone, and I use h2o wireless as my network. I popped the sim out of the old phone (a Samsung galaxy j36v from Verizon) and put it in the 6, and the phone texts fine, as far as I know the data is okay, MMS, etc. However, when I make an outgoing call, there's no dialing tone on either speakerphone or otherwise, yet it still says it is making the call. When someone I'm calling answers, they can hear me, but I can't hear them. Oddly enough, when I receive a call, I can answer it and the speaker and mic work fine, meaning we can both hear each other perfectly fine. So I have no speaker essentially only when I make outgoing calls.
Read more: Nexus 6 outgoing call trouble?