Not sure if you can use the devices in that way.
But you can upgrade the firmware of TL-MR3220 and set correct parameters( such as APN, Dial NO) on the router.
Firmware: http://www.tp-link.com/en/support/download/?model=TL-MR3420&version=V2#tbl_j

See this link for more guidance: http://www.tp-link.com/en/article/?faqid=400