One slight disadvantage of using local SIM’s is getting messages like this from VN MobiFone:
Quy khach da su dung het dung luong mien phi voi toc do toi da. Quy khach co the tiep tuc su dung voi toc do thong thuong hoac gia han goi cuoc de su dung voi toc do cao.
Translation by Google
Rules for using out of space for free with maximum speed. Customers can continue to use normal speed elephant or extension package for use with high speed.