Yes, as long as you're not encrypted. You have to capture the packets on the network. The easiest way to do that is to mirror the port(s) on the network switch where the gateway card(s) are located. You cannot use Direct Media Connection on the phones or the voice will bypass the gateway. Can't really recommend any freeware, but I can tell you that Wireshark will capture and decode the audio streams. Great for diagnosis.
LoPath
Maintain HiPath 4000 V5 & V6, OpenScape Xpert V4, OpenScape Xpressions, OpenScape Contact Center V8, OpenScape Voice V9