With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cGgsnExtActivatedMs
cisco Gateway GPRS Support Node Ext Activated Ms
1.3.6.1.4.1.9.9.647.1.3.3
This object indicates the current number of Mobile Stations with active PDP contexts.
Back to CISCO-GGSN-EXT-MIB MIB page.
IPHost Network monitor allows you to monitor cGgsnExtActivatedMs on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco routers right now.