tai sao EVN ko nang cap tan so su dung mang CDMA tu 450MHZ len 1800 MHZ hoac 1900MHZ de cho khach hang su dung duoc dich vu tu cac loai may dien thoai thong dung co ban tren thi truong . neu ma nang cap duoc tan so nhu the thi toc do tang truong va phat trien khach hang cua EVN that la kinh khung vi mang luoi phat trien rong , song khoe , gia cuoc re , che do bao hanh va cham soc khach hang co mat khap noi