Going from memory, Vonage won't port a tollfree number will they?
Even if they do, my understanding is that tollfree numbers are pulled by the new telco, no action is required on the part of the losing telco, so if you do transfer away, unless Vonage actively fights you it shouldn't be a problem.
Neither the FCC nor the CRTC takes kindly to a company blocking porting of tollfree numbers.
Like a lot of husbands throughout history, Mr. Webster would sit down and try to talk to his wife. As soon as he'd say something though, she'd fire back with, "And just what the hell is THAT supposed to mean?" Thus, Webster's Dictionary was born.
[TELECOM Digest Editor's Note: No, Vonage will not port tollfree numbers *either way*, in or out. Vonage claims to own the tollfree numbers they offer out for assignment. Nor will they port numbers which started out with themselves. The only thing you can _possibly_ do is take back a number you ported in to them to start with. PAT]