wvdial:
(call via: sudo wvdial umts)
(replace <user> with user-name and <newline> with an empty line (separator):
insert to  /etc/sudoers:
<user>  ALL=(ALL) /usr/bin/wvdial
insert to  /etc/wvial.conf:
[Dialer Defaults]
Phone =
Username =
Password =
New PPPD = yes
<newline>
[ModemUMTS]
Modem = /dev/ttyUSB0
Baud = 460800
SetVolume = 0
Dial Command = ATDT
Init1 = ATZ
Init2 = ATM0
Init3 = ATM0
FlowControl = NOFLOW
<newline>
[Dialer umts]
Username = eplus
Password = grp
Phone = *99#
Dial Command = ATM1L3DT
Stupid Mode = 1
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Init3 = AT+CGDCONT=1,"IP","tagesflat.eplus.de"
Inherits = ModemUMTS