Draytek 2750 required by some ISPs.

Vigor2750 Series User’s Guide
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SIM PIN code Type PIN code of the SIM card that will be used to access
Internet.
Modem Initial String1/2 Such value is used to initialize USB modem. Please use the
default value. If you have any question, please contact to your
ISP.
APN Name APN means Access Point Name which is provided and
required by some ISPs.
Modem Dial String Such value is used to dial through USB mode. Please use the
default value. If you have any question, please contact to your
ISP.
PPP Username Type the PPP username (optional).
PPP Password Type the PPP password (optional).
Clone MAC Address It is available when the box of Enable is checked. Click Clone
MAC Address. The result will be displayed in the field of
MAC Address.
After finishing all the settings here, please click OK to activate them.