BB Bold 9700 :: Enterprise Activation - Service Connection Is Unavailable

I acquired an unlocked T-Mobile blackberry 9700 late last year and had our IT admin guy in NY adding new user license to the blackberry server and then the besadmin had generated activation password for me. I'm using local mobile phone network in Vietnam (Vinaphone) and had installed its service book into my BB. Nevertheless, after having put in my email address and keyed in the activation password, after pressing activate for about 2 minutes of "Acquiring service connection..." my BB keeps on telling me that "Activation request failed. A service connection is unavailable" although the communication receptions signals from my local mobile carrier is strong and I can browse internet and accessing gmail or yahoo mail using my BB (which mean internet connection is available).