u should connect your lan cable from another 3G router yellow color lan cable port  into this tl-MR3420 router blue color lan cable port

direct insert and updates list 

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Added on October 27, 2012, 1:09 pm

yes both can support,

if u worry,u can update router firmware to latest 120523 for V1 ~ V1.3

and download modem bin file from tp link websites and upload the modem bin file into your modem setting under network -> 3G

that's your personal choice,

for me, i would prefer V1~ V1.3 due to

can flash with openwrt

and V2 is not support by open wrt, plus the stock original firmware is quite buggy sometimes

and consistency is  as superb after using with openwrt

[attachmentid=3123181]

after i flash with open wrt, sometimes the IP i can keep until 5~7 days before it DC.

with stock firmware last time, i DC every 12~24 hour,.. and keep losing all those good IP address,

that's why i personally prefer V1~V1.3

just my feedback experience with openwrt compare with stock firmware 

for ZTE MF680, just direct plug int routr it will auto recognize and dial your ZTE MF680 modem