Thank you for that last message. The phones are all SNOM300 devices, however, having rebooted all of them only 2 are consistently going to Not Reg. we have swapped those two out for spare phones, and we appear to be ok. We are not intending to make further changes tonight, so we will see whether we achieve stability. The SIP.log is a file we will now watch for any evidence of wierd behaviour. Thanks again. I will update this post later this week.