You probably already have on place all you need to run ScadaMobile.
To use ScadaMoblie locally you need a WiFi with direct access to your PLC local network.
To use it remotelly you need to be able to access your PLC from the internet. For this you need a DSL or GPRS (3G) router on the PLC side. There is no need for a fixed IP. Remote access is possible from any WiFi spot or through the cellular network. Switching is automatic but WiFi is used first if both are available.
The easiest set up for both Local and Remote connection is a standard Wireless DSL router. The PLC must be wired to the same local network as the router.
For about 2 euro (or less than $3) you can download ScadaMobile Lite from the App Store and try it yourself. I encourage you to do so.