We've recently deployed our first Opengear ACM5004-G
http://opengear.com/product-acm5000-g.html and its
working great. It has cellular (3G), ethernet, USB and
four serial interfaces; you could easily daisy chain a
serial interface to a terminal server if you need more
OOB serial ports.
The setup was very easy; our Verizon rep just required
the ESN off the bottom of the unit since Opengear's already
gone through Verizon's certification process so their
devices' ESN's are known to Verizon as valid for their
network. He asked what plan we wanted, I told him I wanted
a static public IP, two days later we were up and running.
Since this is considered a M2M (machine to machine) device,
similar to alarm systems and other low bandwidth devices,
you can get monthly plans down to $7 for a few megabytes
and up to normal consumer-level 5 gigs for $50/month type
plans. The static IP didn't add any cost.
The device has a cool unique feature where you can set it
to keep the cellular interface 'down' for data as its
normal state so no one outside is trying to break into it
or wasting your bandwidth. Then you send a text message
to the phone number assigned to it and it will bring up
the data interface so you can SSH in. You can configure
firewall rules on it, use key-based auth, change the ssh
port number, etc.