Hmmm, if you have Internet access with that card, why wouldn't you just assign a WAN IP (via NAT) to each switch's LAN IP, then you can just get to them via WAN, which is much, much faster, and more reliable. They switches are password protected as well, so there isn't a huge problem with security. Just my thoughts on the subject, then you don't need a modem any longer.
Mitch
AVAYA Certified Expert