You need to be using the external IP address in order to access the OpenSprinkler outside of the WiFi network (eg: cell network). The other caveat is the OpenSprinkler port must be port forwarded through your router.
The external IP can be found at http://wimi.com or typing ‘ip’ into Google.
To port forward your OpenSprinkler, you will need to identify your router model and consult it’s documentation for opening a port. The default port is 80. Some guides are available here: http://portforward.com/english/routers/port_forwarding/routerindex.htm. If you need assistance let us know.