int configure(char){
The function takes an anonymous argument that can never be used. Why?
cell.print("AT+SBAND=10");
cell.print("AT+CFUN=1, 1");
Doesn't it matter what the response to the first command is?
a=cell.read();
if (a=='+SIND: 11'){
The cell.read() function reads ONE character. That ONE character will NEVER equal '+SIND: 11'. NEVER.