i talk to someone w/ vonage regularly and its much clearer that talking 2 them w/ their cellular
like i said, a provider needs the "good housekeeping seal of approvial", that is they need to be ASNAP certified either by having a voip/cellular infrastructure or to have some kind of an agreement w/ the infrastructure that their native network lacks, morover even w/ that native or combined infrastructure they need to be able to prove that it supports seamless roaming