[SR-Users] How do I allow any user to register? And why doesn't a call reach the other end in my case?

Hi, I'm pretty ignorant about Kamailio, sorry for it and possible terminology mistakes. I'd like to allow any user to register. Ideally, I'd like to make some script (Lua/whatever) function to check some data encoded in a username and allow registering based on that username only. I undefined WITH_AUTH in kamailio.cfg, and it used to work for me; but sometimes I'm starting to get "SIP Progress: 100 trying -- your call is important to us ()" and the call never reaches the other party. Here's a sample of my logs during the failed call: https://gist.github.com/singalen/c343f09b67dcf7731fe0 What is the problem here? I start and stop the clients all the time, so there might be some garbage registrations accumulated. I assume I also need a user registration to discard all his previous registrations? Thank you!