Freshphone would intermittently reject my registration requests.
We are using asterisk. Testing would work for a bit, then asterisk would say that registration failed (status rejected). Then, a bit later, things would start working again.
It could be a badly formed FROM header that's causing you to end up being blacklisted temporarily. Are you using vanilla asterisk or trixbox/freepbx etc?
We are using Vanilla Asterisk with PJSIP (if that makes a difference).
Can you please point me to a place where I might need to look? How will I tell if it is a badly formed FROM?
I also test by calling myself. Could that be a problem?