Hi,
I had to buy huwaei e220 to make 3g usb work. (picked one for cheap £8 - plus v.easy to unlock & free)
It is pretty stupid Dlink does not list what 3g modems it supports. You have to bear in mind this is an "old router" - i think 3years since it came out.
For each 3g modem, Dlink must add the 3g modem firmware to the router - so it just seems that it has not bothered to do so except for the very old e220. It is not surprising as they are still fixing errors in their own firmware 3 years on

Probably best to call tech support and get a definitive answer - it either has the firmware / support for your 3g modem or not ?
Cheerz