check with 611 for the exact dial string etc, then make these two files, 
this is for tmobile, tested with a motorola v300 and v360

-- pppdscript.sh --
#!/bin/sh

/usr/sbin/pppd noauth connect "/usr/sbin/chat -v -f chatscript" /dev/ttyACM0 230400 usepeerdns defaultroute noipdefault user '' remotename tmobile ipparam tmobile crtscts idle 300

-- chatscript --

ABORT ERROR
'' ATZ
OK AT+cgdcont=1,"IP","internet2.voicestream.com"
OK ATD*99#
CONNECT ''

when you use noauth, pppd wants to only be run as root. you can use sudo, but setuid wont work.