Does anyone have a tutorial on getting the trunk to work between Freepbx17, and cucm 15 with the pjsip module. I have done this countless times on the old chan_sip and older versions of cucm. I just don’t see where anyone has really published up to date info in the last decade. Thanks!
Howdy! Welcome to the forums.
You might consider reviewing forum posts by @tmittelstaedt – provider of lots of helpful assistance on this topic. 
Hi All,
The following URLs may help:
CUCM Asterisk SIP Trunk Integration – UC Collabing
Trixbox/FreePBX SIP trunk to Cisco Unified Call Manager 7.X - The Tech Journal
This last is one a list member emailed me:
Note that you SHOULD NOT view this as anything more than a TRANSITION step going from UCM to FreePBX (or vis-versa) The reason why is that it’s not 100% reliable.
I currently have this setup and I get occasional complaints that “I was talking on the phone and the call dropped after 5-6 minutes” Then I go to the desk phone of the person with the problem, make a call out to an extension on the UCM, walk away and then come back 30 minutes and the call is still connected.
I know darn well that there’s some border case involved. But there is nothing I can do about it. If it was 100% UCM infrastructure all under contract I could file a TAC complaint, then spend the next month browbeating techs from India and getting the ticket kicked up the chain until someone with a ton more experience in VoIP than me would put the time into actually identifying the smoking gun. If it was 100% FreePBX infrastructure I could buy support from Sangoma and do the same thing. But you know how hard it is to find a problem that only manifests itself every once in a while, is not duplicatable, and leaves no traces behind? All you can do is guess at what it might be, make a change you think might fix it, then give it a few weeks and see if the complaints die down. Then if not, wash, rinse, repeat. And users are notorious for saying stuff like “It’s a huge problem” and then you come to find out the problem happened one time a month ago and never since you made the last change that may or may not have fixed the problem.
A user’s perception that a system is unreliable is formed INSTANTLY by ONE incident, and their perception that a system is reliable takes SIX MONTHS at least to form, and only if the system has worked PERFECTLY every single time for that 6 months. This is the case with phone systems, cars, and computers, basically - everything out there.
Ultimately, I’m going to replace our UCM. But I want to give the Asterisk system a year of time to “proof” it out.