With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
c3gModemState
Cisco 3G Modem State
1.3.6.1.4.1.9.9.661.1.1.1.3
Cellular 3G modem state, up(2) indicates modem can be detected and down(3) indicates modem can not be detected.
Back to CISCO-WAN-3G-MIB MIB page.
IPHost Network monitor allows you to monitor c3gModemState on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco firewalls right now.