I have a few Polycom 650's with the latest public firmware and bootrom that occasionally seem to reject calls. They are all located behind a m0n0wall firewall with a SIP proxy enabled and configured. The Elastix box is in a datacenter. Once in a while, when a call hits a ring group, I'll get these responses back from all phones in the ring group: Got SIP response 400 "Bad Request" back from xxx.xxx.xxx.xxx This only happens occasionally, maybe 1 in 20 calls. Would you suspect a problem with the proxy or the phones themselves? The phones usually ring once or maybe twice before this response is received by the Elastix box.