While it's clear that opening up TCP/UDP1714-1764 would provide access in, it would also be useful to have some way to connect across a VM in NAT mode. Perhaps, if when the Android client goes into "Specify IP address", the client could try to connect to whatever that NAT-Only address, instead of using the UDP broadcast address. I realise this is pretty fluffy and non-specific and probably pretty niche, but it is something I would like to use! :)
Maybe you can make sure the VM is part of the same network? You can surely configure that in VirtualBox.
*** This bug has been marked as a duplicate of bug 464253 ***