|"USB wireless modern [modem]"|
"modem software has a dial-up interface"
The usb wireless modem most likely is a modem router combo.
The dialup you refer to is PPPOE which is point to point protocol over ethernet. This means you authenicate to a server [why you need account name and password] before you are on the internet.
Who told you to buy a 3G router?
You need to return the 3G router since that does not support what you need unless you have 3G service/card you have not mentioned.
Or is this "wireless modem" really a 3G card?
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