I’ve used this configuration, with minor tweaks on 3 different laptops, with 3 different OSes (if not 4) with great success. There’s so little good Linux info on evdoforums.com (at least I have a hard time finding it), and the posts I made link to a site that’s non-existant now, so I realized I had to repost this info. I’ve had both the Merlin S620 Sprint PCS EVDO card, and the Sierra Mobile AirCard 575, and now have a Dell built-in EVDO modem.

For all 3 of them, the only difference was the modprobe line, for vendor and product ID, as noted below.
Merlin S620:
modprobe usbserial vendor=0x1410 product=0x1110
Sierra 575:
modprobe usbserial vendor=0x1199 product=0x0019
Dell Sprint 5720 PCI-Express Modem
modprobe usbserial vendor=0x413c product=0x8134

I saved the appropriate PPP files at /etc/ppp/peers/1xevdo and at /etc/chatscripts/1xevdo_chat. In this post, I’ve blanked out the parts that are particular to my install (phone number), but it should be pretty easy to recreate your settings.

/etc/ppp/peers/1xevdo:

-detach
ttyUSB0
115200
debug
noauth
defaultroute
usepeerdns
user $(full-phone-number)@sprintpcs.com
show-password
crtscts
lock
lcp-echo-failure 4
lcp-echo-interval 65535
connect '/usr/sbin/chat -v -t3 -f /etc/chatscripts/1xevdo_chat'

/etc/chatscripts/1xevdo_chat:

'' 'AT'
'OK' 'ATZ'
'OK' 'ATE0V1&F&D2&C1&C2S0=0'
'OK' 'ATE0V1'
'OK' 'ATS7=60'
'OK' 'ATDT#777'
CONNECT CLIENT

Since I do several bits of work through the console, including accessing my Cisco VPN, and in some cases naim and tmsnc (console AOL and MSN chat) inside a screen session, scripts for these setups work great for me. I wrapped the whole thing up inside a bash script called $HOME/bin/evdo.sh – and I just call that when I want to get online, after inserting the card.
~/bin/evdo.sh:

sudo /sbin/modprobe usbserial vendor=0x1199 product=0x0019
sleep 5
sudo /usr/sbin/pppd call 1xevdo

The sleep statement helps make sure that the modprobe has completed, scanned the device, and settled before calling PPP.

My Dell D620 arrived, and I was able to quickly determine the changes for an “always there” card, vs. a pluggable PCMCIA card.
First I created /etc/modprobe.d/usbserial with the line:
options usbserial vendor=0x413c product=0x8134
and added “usbserial” to the end of /etc/modules so that the card would always come up at boot (sudo lspci -v | less to find the exact product ID and vendor – I only have 2 “Dell” devices on my laptop). I set my radio kill switch to affect only my EVDO and bluetooth radios, letting the software (~/bin/rfkill.sh in Linux and the Dell software in Windows) handle the WiFi – I use WiFi all the time, but only want the battery-draining EVDO in a few specific instances. So I added “cat 0 > /sys/bus/pci/devices/0000\:03\:00.0\rf_kill” to my “evdo.sh” file to kill the wireless when I wanted to use EVDO – no need to ever have them both on.