I couldn't find any info out and about regarding making a Cricket broadband modem work with Slackware so I thought I'd post up in case others are wondering.
Yes, Cricket broadband works like a champ with Slackware. I'm on a fairly vanilla 12.1 install, all I had to do was to
a) plug the USB modem in (Utstarcom UM100c USB modem from Cricket). The required modules autoloaded and created a device /dev/ttyACM0.
b)Set pppd to dial out on that modem, and instant Cricket broadband.
For pppd, your username is your modem's phone firstname.lastname@example.org
(email@example.com), the password is "cricket", and the number to dial is #777.
I'll expand on the details of all this as requested.