So, your Verizon network may be blocking remote access. I did a google search and found this:
Remote access is not possible on the 4G LTE network. The NAT firewall has been designed to hide public IP addresses and ports necessary to support that functionality.
Please see the information and workarounds posted above.
Q. “Will static ip fix or it is just not supported?”
A. Yes. It will cost you a few hundred dollars for a static IP though.
Can you access any other resource or is OpenSprinkler / mobile app the only thing giving you issues?
Update: For the record, Ray and I are working to improve this process and remove port forwarding completely.