Please be aware of a problem in ESXi in which the checksum of UDP packets is wrongly calculated. This will cause the UDP traffic from the SGSN to the BTS'es (vice versa) to fail. It can take quite a while to figure this out (well... to be honest all it takes is a good look at the extended tcpdump output, but hey).

If you experience problems setting up GPRS (symptom: NSVC remains ALIVE BLOCKED), try this command:

ethtool --offload eth0 rx off tx off gso off

(with eth0 the correct interface, or better: for all interfaces).

This works under CentOS (tested) and Debian/Ubuntu (read about it).

HTH/F