Please note that the DLink USB port is for use by a printer/USB drive and <b>NOT</b> a USB Modem.
I tried them all and struck gold with Netgear MBRN3000.
DLink FTP - User manuals:
2760: "The USB ports are for USB storage devices and/or USB printers" (http://ftp.dlink.ru/pub/ADSL/DSL-2760U_BRU_D/Description/DSL-2760U_user_manual.pdf)
2640u: ftp://ftp10.dlink.com/pdfs/products/DSL-2640B/DSL-2640B_ds.pdf (ftp://ftp10.dlink.com/pdfs/products/DSL-2640B/DSL-2640B_ds.pdf)
with updated firmware my 2650 worked with my e220 3g modem