Buffalo WZR-HP-G300NH wireless 3G router and ZTE MF668 3G modem
ZTE MF668 is a piece of hardware that reminds me of children. One day they are just fine and then, another day, nothing but trouble. Most of the time it works, but then sometimes it drops connections all the time.
It is also quite problematic to get it working with routers that accept USB 3G modems. Compared to Huawei modems, which usually work extremely well, ZTE MF668 either does not work at all, or it drops connection, or drops into dead-lock state. I have tested several Huawei modems with Buffalo and couple of Dovado router models, and there is no problem. So it happens that MF668 does not work with Buffalo WZR-HP-G300NH router
As a sidenote, I can recommend Dovado 3GN and 4GR models for average computer user. They are very reliable. Buffalo WZR-HP-G300NH has one advantage to firmware hackers, though. You can easily hack its firmware, and create all kinds of interesting things
Problem is that default firmware in this Buffalo router is crappy. It does not matter, if you are using either Buffalo firmware or default dd-wrt firmware. Neither of these support ZTE MF668. Easy solution to this problem is to use Brainslayer firmware. You can download it from dd-wrt website. Brainslayer firmware is located in Other Downloads section, most recent version for WZR-HP-G300NH is here.
If you already have dd-wrt firmware running in Buffalo, then download the webupgrade-MULTI.bin file, and upload it into Buffalo using admin web-interface. After Buffalo has rebooted, you will notice that MF668 works. I could get easily 10 Mbit/s download speed.