Hi Rad,
External access isn't limited to any particular device, it is how your network is configured to forward the traffic from external to internal.
The PowerLinc (2414) has only one IP/Port interface. The default port is 9020 in the SDM software. In MobiLinc there is only one IP/Port address available to configure access to your 2414. For internal access you would use the IP address of the PC that is hosting the SDM software. If you want to use MobiLinc internally and externally you would enter in the router's external IP address in the MobiLinc IP field and port forward all traffic on port 9020 (assuming you didn't change the default) to the computer hosting the SDM software.
So to recap,
In your router port forward traffic on 9020 (or whatever your SDM is set to) to your PC hosting the SDM software.
In MobiLinc change the IP address to the router's external IP address (found by going to
http://www.whatismyip.com and use port 9020.
Something to consider is in order for this to work your router must support loopback. Most do, but if you have an older router it may not support loopback.
Wes