Safest bet would be for Freethinker to point you in the right direction as ssh seems the safest way.

a quicke google will point you in the right direction, the idea is to dial into your router 192.x.x.x in your browser, again google for the default. In the options there should be an option for port forwarding, some router actually have an option for vnc but another number would be safer... once set, go into vnc options, connection and then change the port number to that of the one you just created. You should now be able to connect to your home machine from outside the network.

Use IPchicken.com to easily find your external ip address and then on your phone the address you will want to use will look something like this, 111.x.x.x:1234 1234 being the new port you setup, note that a ":" is required to seperate the ip address and port number, you will also have to remember that the same kind of thing will have to be used internally.

As I say though a quick google will explain more, I found this.

http://nerdhow.wordpress.com/2008/03...orwarding-vnc/