The big board used to control the motor of my robot , you are so luckly ;), you can use 5v to power modem , it make things very easy , if I live at USA , I will buy one modem like yous , but I in China , the postage is very costly 
The big board used to control the motor of my robot , you are so luckly ;), you can use 5v to power modem , it make things very easy , if I live at USA , I will buy one modem like yous , but I in China , the postage is very costly