The tunnel option would be welcome. I had a chance to try out a WiFi connection during a trip the other day, showed as registered, but there was no audio. I've had that happen when using the 3CX phone on a netbook at various hotspots. Using the tunnel will usually will work, last resort it to VPN in. I suspect that certain ports are either blocked by the owner of the router, or, they are directed to another device on the network.
I also miss the diagnostic menu that the 3CX phone for windows, has. Other than that, it is nice not to have to think about carrying two phones now, when travelling.