Yes, indeed this go back a ways and I recall caveats at the time which Jaron had alluded to back then:
1. Make sure to use the host based mediaload load (starting with "ipvs_evr", such as ipvs_evr_2isdn_net5_311.pcd.)
2. Check your TDM bus settings and make sure the card is set to Alaw. In some builds of the 5.1.1 Feature Pack line, the bus settings will default to Mulaw, even though the card in the system might require Alaw.
I remember the second one being an issue back then.
Regards,
Jeff M.