I used Ultra Mobile for about a year and was happy with the service, then it went way downhill. I stopped being able to receive or make calls in my home: the calls just went straight to voicemail. Other places it worked, but not in my specific neighborhood. I kept calling and complaining, and they kept saying they would work on it. Nothing changed. I requested a refund. They said they would refund half the amount of my monthly charges. While that was being processed, I switched to another carrier. They then rescinded their offer of a refund. So I lost a lot of money for nothing. Don't trust them..
