Did you know that you can use “native” VoIP on your Windows Mobile device?
The forum has the instructions that will allow you to enable your Shadow (Dash or any WM6 device) VoIP over Wi-Fi hidden feature.
I first noticed this option when I was modifying the HTC Wing CommManager and saw an VoIP on/off option.
This feature is similar to T-Mobile’s @home plan. The difference is that you will have a separate phone number. However you can always forward your cell phone to another number. If you have access to Wi-Fi you will be receiving calls and not using your minutes.