Oh, its porting your number thats the problem, I get it now. Implementing porting is expensive for the company owning the exchange. So you can get VOIP, just not keeping your current number. According to:
http://www.fcc.gov/cgb/consumerfacts/numbport.html
Its a state waiver to Union Telco, et al. You might want to file a complaint with the state PUC. Unless Metrocast wants to pick up the tab to fund portability across all of Union's exchanges, there is little reason for Union to give in - might be a long wait.