Allow using facetime from different networks

Hi,

I have a laptop and an Iphone.

I understand that in order for me to make a cellular call, my phone and laptop need to be connected to the same WIFI. (which works flawlessly)

Now question: Can this be tweaked to be able to use the phone without necessarily connecting to the same network? Assuming I forgot my phone at home.. and would like to use my computer to call people. Any community workaround there? like using VPN, hamatchi, or anything else?