Wow the service run by Obitalk is pretty incredible. It has some incredible features using Google Voice and it works with a burglar alarm as well. It also has no FCC fees as well and you can hear your voice mail on Google Voice. Of course who knows how secure any of this is really secure. Using SilentPhone or something like that seems a better choice.
Nonetheless there are a few limitiantions. The biggest one is that Google Voice will not let you port landline numbers. http://offonatangent.blogspot.com/2011/04/how-to-port-verizon-landline-to-google.html has a great trick:
Get a T-mobile prepaid account for the cost of a $5 prepaid sim
Port your number to T-mobile
Then port from T-mobile to Google Voice.