Which version of the HiPath 4000? The pertinent AMOs changed from V3 to V4. Which type of IP Trunking are you attempting: native SIP, SIPQ, native H323, or Siemens H.323 (HFA)?
If there are three systems (2 4Ks and 1 3K), then you must use the LEGK. Do you have knowledge of the LEGK config process? It is not rocket science, but there is a specific sequence to follow - starting with enabling the LEGK. Please re-post with the requested info.